If it's a rope seal, the best one is "Best Gaskets." But they depend on a nice smooth seal area on the crankshaft and proper installation. They also offer a 2-piece rubber seal, but I have no experience with those. LINK
If you're doing a teardown for machine work, get the rear main seal area machined to fit a National #417210 full circle seal. That's my plan on my engine rebuild.

Kevin
1951 Chevy 3100 work truck
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1929 Ford pickup restored from the ground up. | 1929 Ford Special Coupe (First car)
Busting rust since the mid-60's
If you're smart enough to take it apart, you darn well better be smart enough to put it back together.