I've had two fail this month. A Corsair H105 purchased in 2015, and a Corsair H100i from 2013. Not total failure but unusable because temps were spiking to 100C on one or two cores (tested two CPUs and different cooler). The problem in both (I suspect) is that gunk develops over time, and if you move the AIO from one case to another several times as I had to do recently, the gunk can settle in a bad spot and then nothing will shift it other than taking it apart to clean the microfins and flush, which has its own risks. For example, if you get water in a part of the pump block it isn't supposed to be in, it can fry the electronics in there, or leak onto CPU later on because the seal is for the water that's supposed to be in there not for some pockets of the block not meant to have water. Since both coolers were going to be sold as part of used systems, I wasn't about to risk that and potentially have very angry buyers. So as far as I'm concerned they are useless, and I have no need for them myself either. If I get bored one day I'll take them apart.
So if you keep these coolers in the same orientation as they age, and use the system frequently, there is more chance they'll keep working for more years unless the pump itself happens to fail, or your unit suffers more permeation than others.
