So, my in-warranty Samsung m.2 croaked, and it got me thinking about the components' longevity. I updated my PC and now the oldest part there is EVGA AIO CLC 280. It's pushing 5 years, so it is about to be out of warranty. 
 
It had no issues with it at all, but it is now an old device... filled with water. Should I be worried?  Is there a rule of thumb for when I should replace AIO coolers (pumps, radiators)?

Eventually the coolant will evaporate. As said though you would hear the pump making odd noise and the cooler won’t be as effective. If your home is about the same temperature year round I would recommend monitoring the temperature of the CPU and make sure it is not getting hot. By writing down the temperatures in November 2022 you can tell if the temperature is higher in November 2023 and beyond. Of course you need to give a little bit of room for warmer days vs. colder days. It’s also good to know what the GPU temps are normally for your system. It’s a good habit to get into recording after dusting the computer.

Thank you all for your responses. The radiator is mounted on top of the case, so the pump is always full of water. I haven't heard any funny noises from the cooler either. I'll run the cooler for another two years or so. I really don't care if it fails as long as it doesn't leak.