You can replace the rubber seal with a rope seal, Tim. If you have the rubber seal currently, those do wear out and will leak when they do. You normally don't need a Sneaky Pete or anything to replace them. Normally you can push the end with a small screwdriver and turn the crank and have them follow out. If you're curious, here is one which came out of a 1959 235 compared side to side with a new rubber one. I think you'll see why the old one was leaking:
http://i1154.photobucket.com/albums/p535/JonGoodman/rearmainendtoend.jpg This may or may not work for you, but it is a different approach and might be worth a try if you have a rope seal. I did this around 20 years ago on a 1956 Cadillac and while it did reduce the drip it didn't eliminate it. I was years later told the remaining leak was probably from a seeping head gasket. From what I recall, these gaskets leak predictably at the rear of the valley pan and mimic a rear main seal.
I watched a fellow fix a rear main leak in place using a stainless spring steel piece from a windshield wiper blade. It was about 1/8 inch wide and maybe 25 thousands thick. He measured it in the lower bearing recess and cut it, grinding one end tapered and then rounded that sharp edge a bit. Then he slowly drove this between the back side of the upper rope seal and the recess in the block until the ends were flush on both sides. He replaced the lower rope seal in the normal way, put gasket sealer on (the seal piece ends also) and tightened everything back up again. It is all a matter of trying to push the rope seal closer to the crank surface.
Good luck!
Jon
