Had my mecahnic change an oil pan gasket on my 69 cutlass. As you know the motor needs to be raised a little to do this job. Picked up the car and drove it straight home. Everything looked fine, that is until the next morning. I looked underneath the car and there was a 12" puddle of oil under the differential leaking from the pinion seal. I have owned this car for 20 years and it has never leaked from the rear end. I took the car back and we put it on the rack. Basically he said that he raised the engine 6 inches and did not separate the transmission, just took out the two carriage bolts that hold the tranny to the frame. He did not drop the drive line either. Could pressure from the drive line (during the engine raise) to the pinion yoke cause the seal to go bad..? Thanks for your opinions.