Doc here again . . .
What type of manifold are you running? Some of the early type manifolds with the breather at the back for crankcase ventilation were known for leaking
oil but usually only if the engine was developing high pressure internally. Make sure your crankcase is running under vacuum, not pressure. Improper crankcase ventilation will cause excessive presure and
oil will leak out of all your seals.
Also, have you checked the transmission front seal for the input shaft or is it definately an engine
oil leak?
Doc