Since your AIO is known to have a possible fault, if I was to make a bet, I'd bet the AIO is your problem.Or possibly the CPU itself
A peerless assassin is a relatively cheap way to test it, certainly easier than a new CPU or RAM, so that's what I'd look at.
I don't know if there are visual ways to tell the specific fault mentioned in Lian Li's link, but you can often diagnose a broken AIO.