Could be the lock ring not holding tight at the fuel sending unit going into the tank.
If they put a new sending unit in it, it is recommended to use the original lock ring with the new gasket. The aftermarket new lock rings don't fit right and they leak.
The tank is new and sending unit are new. The first shop installed it and the fuel gauge didn't work, so i went with another shop and the fuel gauge still doesnt work and leaks too.
