Cork and old-school Permatex. No RTV, no silicone.

Even Permatex is now fuel-solvent, thanks to Ethanol. The only gasket
sealant I know of that is proof to modern gas and E-18 is Hylomar,
http://www.hylomar-usa.com/
It's hard to find. We sell it at davebean.com , and i heard it might be
available at Harbor Freight.

1/16 paper gaskets should do the job, and cutting them with a hammer is
kinda fun, until you get a job in a shipyard.