I had a cooler master seidon AIO in my fx6300 system for years that worked flawlessly. In fact its still going strong.
Then I built my ryzen 1600 system last summer. I decided to stick with cooler master as their products had served me well in the past. I did really want a Kracken as they look so pretty but I just couldn't justify the extra cost.
So I went with the master liquid pro 240.
It worked fine for 6 months then over the Christmas holidays my PC switched off randomly & wouldn't switch back on, I thought the problem was my PSU so replaced that and the system worked fine for a day then the same thing, so thought they issue was my motherboard. It was only when I got a new motherboard and took the cooler off to install it I discovered this.
People talk about how if your AIO leaks the manufacturer will cover it but when I spoke to them on the phone they gave me the run around. Talking about household insurance, palming me off with the retailer. Then eventually said I could send my system to them in Holland at my own expense and if they discovered it was a manufacturing defect I could take it further.
They wouldn't even deal with a RMA of the cooler and palmed me off back to the retailer.
I couldn't be bothered with the hastle and expense of sending my system to another country for them to weasel their way out, and then have to pay again for my faulty parts to be sent back to me. So I put it down to bad experience and replaced the CPU, motherboard & ram.
I was pretty lucky my GPU wasn't fried. Only one stick of ram was damaged but you cant buy single 8gb sticks of corsair LED.
Cost me £60 more than when I originally bought it 6 months earlier.
I bought a wraith to get me up & running again and today I ordered a Cryorig H7. The lesson for me was stay away from water & cooler master products.
So in my opinion you are right to be paranoid, but then again you could be one of the many that goes liquid and has no issues. But there is always the potential for catastrophe.