Leaky fuel tank at sender..

Well, you could pull it apart and use the rubber gasket to make another thin gasket to compensate.

The gasket you make should not be real thick. Put it back together using the rubber gasket, then the sender, then the gasket you made, then the lock ring.

Essentially what you are doing is taking up some of the space that the lock ring is lacking.

Also make sure the tangs on the tank itself aren't pushed out.

When installing the lock ring, don't use just one tab to seat it, use alternating motions so to keep it centered.