That is precisely why I am looking at it myself. I had an opportunistic shop in Palm Desert CA tell me it was the rear seal. I am now almost positive it is not. It is definately not the valve cover gasket though. It sounds as though there are some connections at the base of the oil filter housing. The housing itself is a bolt on and there is an oil cooler also. Believe me I hope it is something as inexpensive as a valve cover gasket.
1971 Unimog 416