You can also do harm over tightening if it doesn't seal dry, then the gas resistant sealers come in handy.

Permatex #2 is gasoline resistant, and everyone should have it on hand for gaskets already, also good on pipe threads. https://www.permatex.com/products/gasketing/gasket-sealants/permatex-form-a-gasket-no-2-sealant/

And this is the other I was thinking of, Leak-Tite Blue http://www.laco.com/pipe-thread-sealants/leak-tite-blue/

This I've heard is good but haven't tried myself, RectorSeal No. 5 http://www.rectorseal.com/rectorseal-no-5/

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-