re liquid cooling systems
I've seen several which leak, and all the rest seem to lose fluid through evaporation.
The leaks aren't helped by the fact that the cooling solution is usually a water / glycol mix and seems to find weak joints very easily.
Topping up the reservoir can be a right PITA, especially if (as on some) the system doesn't prime properly and you have to try to draw out the air locks by bending / twisting the pipes.
Not worth the grief in my opinion