As a rule I like to keep joints with gasket in them clean, once you start using goo inthem you'll have to keep using it and it can be a liability sometimes, my LSE likes to blow the stuff everywhere.
I also don't bother with it on sleeved (scarfed) joints but maybe I should :-k
So if the matel either side is new then use a new gasket only, use assembly paste on sleeved joints like Steve says and on older joints use a bit of common sense, I know you have plenty ;)