I always used permatex non hardening sealant on paper gaskets, I believe it's a locktite product now, aviation non hardening sealant. Handy especially on water galleries etc where there is a chance of previous leakage and therefore pitting. This stuff stays tacky. I also use Stag on welch plugs too.
Ideally you should not have to use anything, however on old bits I usually do. Beats using half a tube of ultra blue on everything.
JD