Gas tank leak

The factory rubber gasket always worked best for me. The dealer should still stock it. Another area often overlooked on sender leaks is the steel fuel line that goes through the sender plate. The soldier connection there is prone to popping loose. Also, on A-bodies especially, many get pin hole rust on the upper surface under the trunk floor. You have to pull the tank to check that. Don't forget to reinstall the insulation pad. Usually you can see where the leak is as it will leave a fuel stain.