I would add if you are using the nails with the side seals make sure they are flush or slightly recessed. Sometimes they need a little shortening.
JKG gave you a pretty good rundown on the procedure but I have never had to fight getting the rear main cap loose. Definitely check for the leak elsewhere because they all (valve covers, intake manifold, distributor,
oil filter adaptor, etc.) drip off the back of the motor. Good luck!!
John