People around here are using RTV silicone, epoxy etc I think. Ive seen some articles on overclockers.com of people using a rubber gasket style seal - I guess with these rubber type seals, you could just make one, throw it together and run it for a few days and see if it leaks. Id check it every few months though, if i made one, depending on the type of rubber.
I'm sure one of the whores around here will help you more that this tho
(yes, you know who you are)