Rear Main Seals ?

GM service manuals showed how to repack the upper rope with a tool that bolted in place and a punch the same shape as the seal groove. We never used it but I did have success just with a punch packing the upper seal tight and adding material from the old lower seal until it was too full to get any more in,then replacing the lower part with a new seal. There was a sneaky pete that worked like chinese finger toy(gets tighter when pulled) made of fine wire that grabed a new rope to pull it in. There is really no reason a 2 piece wont work. If you loosen all the mains a turn or 2 the crank will come down far enough to make it easy to slide in. If you dont you will peal the outer surface of the seal some. I like an anerobic sealer if the seal is contained in a main cap or RTV on the BB style. You want to seal the rear cap without holding it from seating in the block. On a BB the seal retainer plate can best be sealed with RTV in my opinion.
If you find a sneaky pete at least drop the crank a little and after installing a new rope and torqueing the other caps cut the edges flush with the block. Use a pipe or large socket on the lower rope to flatten it as much as possible and then cut off the ends flush.
It aint easy or fun and oil will drip on you no matter how well you clean it.