Leaky Petcock Questions

[Dr. Frankenstein]

I recently had to re-drill the petcock holes on my CA95, and decided to replace it with a flat, round piece of aluminum, drilled and tapped to take a cheap fuel tap.

That works great, but fuel is managing to leak out from the tank and in between the cork gasket I'm using and ruing the paintjob.

Is there any good way to make sure an aftermarket (or fabricated, in this case) petcock won't leak? Gasket sealant, maybe? Although everything I've seen so far says to not use in direct contact with fuel...I'm thinking about JBWelding it; do I have any other options?