If you want to seal it....& never worry about it again, use silicon only, no other gasket.
Put a nail in the wall, paint 'Antique' above it, & hang all your cork/rubber gaskets on the nail....
To use silicon effectively: thoroughly remove all old gaskets, use knife if needed. Clean surfaces with petrol, final wipe down with lacquer thinners. Do not over tighten, silicon will get into the threads & acts as thread sealer.
I don't bother with expensive silicon, just use the cheap Parfix neutral cure from Bunnings.
Being doing it this way since 1978. Or was it 1979.....