The rear pan gasket. Did not think about it. Now I did this. I took off the dust cover which was filled with oil. I crank up engine and layed up under truck with a flaslight and wacth the spot at back of motor where seal is while engine was running. I could see no leak. But I did not look at pan at all. Really don,t know if I can see it. At that time, I felt like the main seal was not leaking. But when I drove truck to work today. After work I looked up under truck and seen a big spot of oil. checking further, I seen it was driping from the little hole in the dust cover. That when I detrunon it was indeed the rear main seal. If you drive the truck 50 miles you could loose about 1/4 to 1/2 qut of oil I drive about 80 miles a day so I,m loosing about 2/3 to 1 qut. a day. Thanks, John.