I recently replaced my 2005 Ford 500 fuel rail sensor. I followed the instructions by using the enclosed grease around the o-ring and reinstalled. Seemed okay but started to smell fuel and checking found that the sensor was leaking.I thought I might not have tightened it enough - and now have complicated the replacement with a stripped bolt. That is not my concern as I will repair that mistake. My question is why the new fuel sensor was leaking in the first place? Does it require a gasket? Should I apply the grease on the entire surface or what?