My 78 L82 PC Rear Main Seal is leaking. I would like to replace it without pulling the engine as I understand the engine has never been removed or had any major repairs. Is it reasonably possible to replace it with the engine in the car?  If so are there any videos or other instructions on how to do it?  It would be great to hear from someone that has done it. 

I have a 79' L82 and I just replaced the rear main seal and main bearings without pulling the engine. You have to disconnect the steering linkage where it bolts to the frame on the passenger side in order to drop the oil pan.  Remove the rear main bearing and loosen the other three main bearings to take some pressure off the seal. Its a two piece seal so the half in the bearing comes right out. You can try a punch to get the upper half of the seal out or buy a seal puller. Its a wire with a cork screw on the end that you screw into the seal and pull it out. Mine came right out.