gas tank sending unit

OK I'm going to guess what you'll find inside... If its the OEM sender with square box, The sweeping contact in the sender was originally shaped like top half of a bagel. This would keep it in contact with 2 or more of the resistor winding laps. Since we have weaker brass sweeping against nickel chromium wire the contact eventually wears through to become a fish hook shape. Then it snags a winding lap and stays there. If the winding had stayed flat against the board its wound on the snag wouldn't happen. The wire didn't grow in length, the board shrank.
The half moon shaped box collects trash inside presenting different result/condition.