I had a similar problem with my mustang.. I thought it was the tranny, but it was a result of excess crankcase pressure. Oil was pushed out of pretty much every seal on the engine and ran down the back of the engine onto the transmission, headers, etc. I would get a can of engine bright, clean the engine and watch for the leak. If I had to guess I'd say it is from the back of the valve covers, and would check the PCV system's function (ensure that vacuum line draws vaccuum, check for clogs etc).