[Ieatcamaros]

I assume you are talking about a fox body mustang here. These cars have a one piece rear seal which you can change by pulling the transmission. If you have to change the oil pan gasket, then you will at least have to lift the motor up a few inches. Sounds like the rear main seal to me, though. Don't count out the intake gasket either. I am talking about the cork gasket that goes along the lifter valley at the back of the motor between the heads.