I also order spares, but the newer black ones are different from the initial design so if you got one of the earlier blocks then this would be something that user should consider.  
 
I ordered two gasket kits in both white and black before I knew only the blacks are different.  I also ordered replacement gaskets right after I got my blocks so I guess those are now pretty much useless but I'm okay with that.  I also ordered a couple of their thermal pad kits as well.  I kinda wish they would have pre-cut them for us but it is what it is.  
 
I am gaining confidence in the block after seeing the impact the new gaskets had.  I know I pressure test to a higher psi then I need to, but I like having that knowledge that it will hold.  These new taller gaskets really are that much better than the original ones I have.  I wasn't feeling a rush to get my kingpin in before I got the gaskets in.  Now I'm wanting to get the parts in I need to help support the weight of the block in my build more than ever.  I'm still going to be doing additional pressure test since I can't mount my gpu until those parts come in.  I have to do a little bit of drilling in the case to mount the kit I'm planning on using to help spread the load of supporting this block so I really can't do much until it comes in anyway.  

For those that have the block, did you clean your gaskets prior to running the block? The reason I ask is that there is some oil seeping from the gasket.

I am undecided right now. The back I'm not worried about since you can't see it on my build, but on the front you can see the excess gasket oil. I may reach out to Optimus

The oil helps hold the gasket into place when they assemble them and also prevent the gasket from drying out over time.

I've just used a thin layer of Vaseline.. even on the inner orings on my ek hardline fittings so the tubing slips in easier without damage to the oring.

O issues over the many years.

As long as you have the newer black gasket in you should be good with a single test since it takes up more of the gap area where the gaskets sits.  The original gaskets are shorter and I believe that is why they pass the initial test where they are still holding their original shape better but over time and tension they flatten out thus reducing the amount pressure they have to seal up against both the block and the plexi.  The difference between the two is very noticeable as I was one of those who got the block early and had issues with leaks even after my block passed initial pressure testing.  There were also a few others who had similar issues with one user who documented the amount of leakage when he took apart his loop for maintenance. 
 
The new gasket is a night and day difference and when used it compresses to the whole width of the gasket channel while still maintaining the seal.  I was pressure testing with my original black gasket for about a week recently and was still having a slow leak issues when testing under high pressure.  I took a chance and ordered both new black and new white gaskets from Optimus.  When they came in I could immediately tell the difference between the white and black gaskets.  I emailed Optimus about this and they confirmed that the white was still the original design and the black was redone with different dimensions.  I put the new black gasket that I received recently in and the leak was greatly reduced when testing at a very high .75 bar.  The amount of air pressure loss was about .02 bar over about 6 hours or so with the new gaskets.  This test was done above the recommended pressure to see if it would hold.  I have run full system pressure tests in the past with the Optimus block for my 3090 and my son's 3080 and they passed without losing any pressure.  I did two extended tests at .75 bar and the results were similar with about a loss of about .02 bar over the course of 4-6 hours. Yesterday I ran the pressure test at around 8pm at approximately .6 bar and after about 4 hours it was still at or near the same reading.  I left it overnight and checked it this morning before I went to work and pressure remained the same.  
 
I would recommend double checking new blocks to make sure the cold plate is secure before mounting it to the gpu.  After completing the block conversion pressure testing alone would also be strongly recommended but it does seem like the new black gaskets are holding up fine. I would also double check and torque down the plexi plates to make sure the gaskets compress and seal well.  You don't have to over do it, but make sure it bottoms out enough to ensure a prolonged and stable seal.  

USMC1419
I may have spoken too soon. Take a look:
 
https://imgur.com/a/ZKK05Dm

Mine isn’t seeping. I covered up my holes before the install.

USMC1419

AtozGlue

USMC1419
I may have spoken too soon. Take a look:
 
https://imgur.com/a/ZKK05Dm

Mine isn’t seeping. I covered up my holes before the install.

What do you mean covered up your holes?

Mine just started seeping at week three.

Ouch.
 
Week three is about when I noticed mine was seeping too.  I'd pull it and check the card to be safe.  Another easy place to check is under the OLED display.  I found a significant amount of water under the OLED.  I also found when I loosened those screws down the middle, some water would come out.

USMC1419
I added more photos to this link, I pulled the card out.
https://imgur.com/a/ZKK05Dm
 
I can't tell very well where the actual die is, if that is water or just residue from the pad. The pad does seem "wet" but I'm trying to figure out if it's too wet (water) or just the residue to be expected, but there's no doubt this is coming from this backplate side. 

Why is your cold plate red? That pic is confusing. Why does it look like your ihs came off.

I didn’t see the earlier replies but I would follow the checks that fragility went through.

With the new gaskets I needed to install mines so I bottomed out screws when I was putting the block back together. I’ve had my block under pressure now for almost two whole days. I wanted to do the extended pressure test to see what would happen and so far it has held all pressure with no leaks at approximately .6 bar.

This is after numerous shorter test to see it maintain pressure. I’ve been ruining .75 bar pressure test for 4-6 hours. Usually the loss of pressure was around .02 bar over that period of time.

The newer taller gaskets which only come in black seems much better. The difference between the old and new gaskets is obvious when you bottom out the screws that hold the plexi to the mid plates.

USMC1419

AtozGlue

USMC1419
I may have spoken too soon. Take a look:
 
https://imgur.com/a/ZKK05Dm

Mine isn’t seeping. I covered up my holes before the install.

What do you mean covered up your holes?

Mine just started seeping at week three.

https://imgur.com/a/kQyHU3X

I used a hole puncher and vinyl wrap. Made stickers. Covered all the screw holes on the backplate that isn’t required to mount to the mid plate. After the holes were covered up. I applied the rear thermal pad. This will prevent any oil seeping through the threads of the backplate’s screw holes.

USMC1419

AtozGlue

USMC1419
I added more photos to this link, I pulled the card out.
https://imgur.com/a/ZKK05Dm

I can't tell very well where the actual die is, if that is water or just residue from the pad. The pad does seem "wet" but I'm trying to figure out if it's too wet (water) or just the residue to be expected, but there's no doubt this is coming from this backplate side. 

Why is your cold plate red? That pic is confusing. Why does it look like your ihs came off.

Cold plate is fine, it's just the reflection of the light.
 
I did find a few loose screws on the backplate when removing all of them to take a look at the gasket. Not sure if that was the culprit or not. I'm letting it all air dry tonight and I'll see what I can figure out tomorrow. I already emailed optimus. 
 
Now with the acrylic piece off the backplate itself, the backplate does look slightly curved. Not sure if I should have them replace it or not.

Yikes.... When the backplate has a bow to it, the mounting pressure across both of the blocks is affected. I disassembled and reassembled six times, doing a full loop teardown before giving up only to discover my backplate was bowed. I also noticed seeping through some of the bends on the gaskets.

No way in hell would I trust this block in my machine for a daily driver.

 
To me this looks adequate, but not sure if this is the original or new version. I got my block fairly recently so I'd hope it's new. Others have said what I am seeing could be seepage from the oil of the pad itself.

Yes I do, I'll measure when I get home. Really seems to be that this is the oil seeping from the large thermal pad luckily because the oil/meister that I thought I was seeing was already underneath the thermal pad on the PCB which would have fried it by now if it actually was water.

The gasket channel and how the original gasket sat in it was a cause of issues for some of us who got early blocks. It’s hard to gauge the gasket by looking at it on the plexi since that is flat. The older gasket when put into the channel did not fill the entire width of the channel machined into the plates. The newer seems like it is a tiny bit wider but I know for sure it’s taller then the original so it has more material to compress and fill the channel thus maintaining a more consistent seal after the gasket starts to compress more over time.

If you had the opportunity to air pressure test your block before you disassembled it and after you had a chance to fully drain it that might have helped isolate the issue and where the leaks are coming from. Mines for sure had a small leak on the cold plate more than likely cause be either debris in the finish or not enough compression. I had coolant on both sides of the oring for the cold plate and I found that one of the screws was loose. Recently after I got my replacement mid plates in I had been pressure testing the gpu with the new mid plates. For shorter tests it help air pressure pretty stable. I ordered and replaced the original gaskets with the new ones and found the new gaskets to hold pressure much better overall. The leaks were greatly reduced under high air pressure testing. At .6 bar the block has been stable holding pressure for over 2 days going on to the third.

I Think in your case I would check the screws compressing the plexi to the mid plates and tighten them down a bit more.

Fragility, that looks a lot like this:

https://imgur.com/a/VnrTCdG

Which could be a bubble or just oil. I feel if that was a water bubble the entire center channel there would have water and my system would have fried being a center screw over the PCB. I was running the PC when I saw this and immediately shut it down.