My first post, be gentle....
My experience from re-occuring rear main seal leaks are caused by the following; (1). Not enough crankcase venting. Guys buzz motors up to 7K with a PCV valve and a vented
oil cap.... Popped out intake gaskets and leaky rear mains! Crankcase pressure has to go somewhere....Doooh! (2). Not enough lube on the seal at start-up... Dry start-ups will pour
oil instantly, but slow enough to leave a 6" diameter of 20W50 on the floor after a romp! Use plenty of Moly assembly lube on the rear seal. (3). Not the seal at all, but a leaky intake gasket, block plug or rear camshaft plug, Flywheel bolts should be sealed, on factory SB motors, the holes for the flywheel bolts go all the way through into the crankcase.
Respectfully disagree with the previous poster concerning a 2 piece seal "as good as" a one piece... No way, Jose'! IMO, one piece seal is far superior than a two piece split seal. I believe 1980 and newer Windsor and 5 Liter engines carried the better one piece rear main seal.