I have a 64 c10 in-cab tank and I can't get the sender gasket to seal for long.

First I tried Aviation Form-a-Gasket Sealant - lasted ~1 month then started seeping.

Second I tried Permatex #1 - lasted ~6 months and now it's seeping again.

I'm using the rubber gasket that came with the new sender. Is there some other gasket material that'll work better? Is there a better gasket sealer?

Tanks!
Terry