Have 1993 Mercury Grand Marquis. Has oil leak above oil sensor and looks like bolt holding on oil filter housing, that bolts to block. Seems od, but not coming from anywhere else. Bolt is tight,

Very possible the diaphram in the sensor has a hole in it. Replace the sensor. Do you have a guage or just a idiot light? Look around the sides of the sessor to see if it is wet. Wipe clean, restart and run at fast idle for approx. 5 min. then recheck for oil leak.

I should have told that I have already replace the oil sensor switch. It is coming from the bolt, holding the oil filter housing to the engine block. It leak severely when started up. Bolt is tight. It is coming from base at washer on bolt, going into the engine block. Cannot figure why it is leaking from there. It that bolt going to any oil supply on engine block?

I am confused?? Arer you telling me that the oil filter is not a spin-on type? But is a "Canister type" and there is a bolt to remove the filter on the bottom of the filter? If this is so, there is to be a fiber seal washer at that point. Also a seal on the top of the canister. And yes, since it is coming from the filter it is tied into the oil gallery on the return side returning the oil to tank. I will wait your reply!