"I did not see any potential oil leakage in that area before I started."
Was the engine recently running before you bought it?
If it was, and if it was/is not leaking, . . .
Nonetheless, Best Gasket sells good rear main seals (rope and rubber).
http://www.bestgasket.com/engine_catalog_years.asp?YearsCID=1953-62,%20235.......[543]
They say rubber seal for a 1956 235/261 - maybe others will post comments..
