I replaced my old nonworking sending unit on my 51 with one that came with a set of gauges I got from a vendor and everything works great but I've had problems with the sending unit leaking from the mounting screws not from the gasket under the sending unit but from the screws ? I've tightened them and it's ok for a few days but then they start leaking again. The screws all have small o rings on them and for whatever reason I can't get them to seal, can anyone think of anything I can do to stop this ?