Odds are you are wasting your time replacing the plug. The problem is likely corrosion or dirt. Use a pencil eraser to rub the spring wires inside the jack - be careful not to distort the wires. Rub the contacts on the plug too. Put a little dielectric grease on the contacts to prevent corrosion.

This type on connector has no business being in a marine environment. It is there only because it is cheap and the cables are cheap.