I was just thinking wouldn't something brake after a while? A pump and other things carrying water in circles for hours at a time in someones computer while playing battlefield 3 . How long would a custom loop and a closed loop last?
Corsair offer a 5yr warranty on their coolers, so it would make sense they would last that long. Though it is always a possibility you receive a unit with a defective pump that breaks after 5 minutes or a whole year. You can never really say for certain if it will last.
But at the very least I would expect it to last 5yrs before it dies of "old age". If it does, then you get a brand new unit and warranty.
A custom loop is much harder to say because you have so many different component makers, there's the greater possibility of user error and for something to be used in a way not-intended. So it would come down to the quality of the parts used and whether the person building it knows what their doing.