[WYT VNM]

Had this same problem with my Unique. It makes for a smelly trunk. Solved the problem. When the sending unit was mounted, the several mounting screw holes had "puckered" up. The gasket was not able to do it's job. Had to empty the tank, remove the sending unit, carefully place secure tape INSIDE the opening to prevent anything going in, flat filed the "puckers" on all screw holes, carefully removed the tape, replaced the gasket, fixed!

Before you re-gasket or sealer, make sure the screw holes are flush with the surface of the tank.