Nearly killed this the other day. I changed the fans in the top without turning the system off as it was busy downloading something and I needed to send off the top fans.
I took all 8 screws out, and while I was looking for the other fans I suddenly remembered that the only thing holding the radiator to the roof of the case was 8 slightly warm rubber washers. You should have seen my face!
Luckily it stayed stuck there.