dmford,
I fought a pesky
oil leak in my pre'81 408W block and finally put a sleeve on the crank effectively increasing the diameter .009" and it works fine!! Fel-Pro sells it as a "Redi-Sleeve" and others make them as well.
A product that does a great job on old, dried out seals is SealLube from New Technology Int. Phone: 810-758-3220.....Give it a try!!
Good Luck,
Coosawjack (aka-Cobrajack)