We use 'por-15 in the shop all the time for bike tanks. Works real good.
http://www.porcan.com/usa/tanksealfuelpreserve.asp
I have never used the 'kreem' brand, but it is probably the same kind of thing.
Regarding your clutch, sounds like the plates are stuck together? If it has been sitting that long, no doubt they are. Dissasemble the clutch and have a look.
