SB rear seal leak question

OK, Small Blockers, maybe somebody here has a solution for me!

A while ago I had a race 340 built for my Barracuda out of the modern 4 bolt main "Resto 340" MP block, and an early style forged crank. My builder told me that the early and later Mopar small blocks and cranks used different types of rear crank seals, and he installed the latest type crank seal in this engine, despite the early crank. "It might eventually leak", he said. So, a couple of years and a few road races later it appears to be leaking, pretty profusely.

Anybody else running this mis-match of crank and block, and how did you solve the rear seal problem? I hope you don't tell me to change the crank! :banghead:

Thanks;

Mike
Scappoose, OR