leaking fuel sending unit

Some sealants are incompatable with gasoline. they can swell up many times their original volume.
A friend of mine rebuilt a fuelpump on an aircraft engine.
He put a little skim coat of RTV on the new gasket thinking that "it couldn't hurt".
The airplane only got 100 ft in the air when the engine quit and had to land in a bean field. Lucky landing with no damage to the plane.
The fuel line and filter was plugged with gelatanized RTV that seemed to be nearly 50 times more than he had used. maybe even into the carb.
I know they had to do a teardown on that just to be sure.

So no RTV on anything near gasoline for me.