Rads are the hardest to clean. They could still be caked plasticizer and for a long time. I would just scrap the old rad and keep with the new unless you're definite that it is cleaned and not spreading plasticizer to the rest of the loop.
I will echo what some have already said.
- Loop order doesn't matter. Res before pump is the most important and just cleaning up your route. If you're looking for a 1-2 temp difference, maybe going to the CPU first and than the GPU since CPU's are the most sensitive.
- Don't use Silver coils or silver based biocide since it can or will conflict with EK's nickel blocks. EK has been warning about this. You should still use a biocide as growth can happen to anyone and its not pretty.
- Use clear premixed fluids from reputed companies. I personally use Clear DP Ultra from Aquacomputer and has worked great.
- Only use PrimoChill Advanced LRT since it is plasticize-free. The older models can be plasticized so I would just scrape the old "Pro" model you have there.
- Keep an eye on the loop for deterioration for the next several weeks as it will slowing bleed itself out. Might need a refill here and there.
Last but not least, show us some pics of the rig.
