Sending Unit bad?

To the hash marks on your stock gauge 10 ohms is full 73 ohms is empty.
Greater than 78 ohms = no needle movement from its home position.
Less than 9 ohms will overheat the gauge.

If a brass float has been bouncing against the bottom of a steel tank for a long period of time, of course it has a hole in it.
Dents in the tank can be corrected with air pressure and a rubber hammer. How much air pressure is a gamble. Enough p.s.i. to move the dent might sooner bust a seam.
Good luck with it.