Old or New Fuel Sender?

Both senders have their pros and cons. The original sender would bounce the float against bottom of tank. Eventually wears a hole in the brass float.
Lift the side of the electric housing open to view inside. You'll likely find the board has shrank with age and now slack in the winding has let it lift away from the board.
The scrubbing contact should be shaped like top half of a bagel for lack of better description. When that wears into a 'C' shape it hangs the loose winding like a fish hook would.
The aftermarket sender of later design isn't as accurate and the half moon shaped electric housing will collect trash in the bottom of it.