First I wanted to say thanks to 1lugloose for his post. I had the same problem with my 2000 Mustang GT today.
I could clearly see oil and even coolant dripping from the oil filter housing. Also my oil pan was obviously covered in oil as well. I am hoping the oil pan seal is fine and it was just blow back from the leaking oil filter housing seal.
Total parts costs: $65.00 (That's including the Oil Filter Adapter Gasket, Engine Oil and Oil Filter, shop towels, and the coolant for the radiator.
Approx time: 5 hours (That was taking it nice and slow to ensure everything went well and cleaning as much of the old oil off of the bottom of the car.)
Here were my steps:
1. Removed the radiator and oil filter caps.
2. Drained the oil and removed the oil filter. I went ahead and placed the oil pan drain bolt back in so I wouldn't forget.
3. Drained the radiator coolant via the plastic plug on the bottom passenger side of the radiator.
4. Removed the radiator hose from the bottom driver side of the radiator that runs directly to the oil filter housing. (This hose has three connections)
5. Removed the four 13mm bolts from the oil filter housing.
6. Removed the oil pressure sensor from the oil filter housing. ( I assume that is what it is called. In my case it was so oily that I could not get the clip off so I had to unscrew the entire sensor.
7. Next I took some fine sandpaper and cleaned the oil filter housing and where it mounts to the block to remove what was remaining of the old seal after removing it.
8. At this point I was able to un clip the sensor.
9. I cleaned the sensor threads and sensor clip and then tightened it back down onto the oil filter housing.
10. I carefully placed the gasket back onto the housing. I was not as lucky as my bolts kept falling out while trying to align it back to the block.
11. Counter Clockwise I hand tightened each bolt. I then applied some more pressure to all four bolts. Finally I made one more round completely tightening down all four bolts.
12. I hooked the radiator hose back up to all three connections.
13. Screwed on the new oil filter.
14. Inserted 5 qts of oil.
15. Inserted the coolant and topped it off with water.
16. Finally, the moment I was waiting for, I started the car and crossed my fingers lol.
I let it run for a good 15 minutes while watching the radiator coolant and the dashboard gauges. Finally I peeked underneath the car and the oil filter housing was completely free of new oil
I hope this helps someone else!! I'll check again in the morning to make sure there are no leaks.
P.S. While underneath the car I used a 10mm ratchet and snugged down the oil pan bolts in hopes that if there was a leak there as well it may stop it.