I have a pretty bad oil leak at the rear of the engine on my 1941 Chevy AK.  It has a (I think) 1954 235 engine that came out of a Chevy car with a 2 speed automatic transmission. I tried to replace the seal with a rubber seal I ordered from Jim Carter parts and I couldn’t get the old seal out. It had been replaced by the previous owner with a rubber seal and it looked to be in good condition. I took the truck to a local garage that had previously rebuilt the transmission. They put in the new seal from Jim Carter and it still leaked. They ordered a new rope seal but it was too wide and wouldn’t fit. They ordered another rubber seal from Chevy’s of the 40’s and installed it. It still leaks. I have replaced the valve cover gasket and the valve tappet gasket and there are no leaks from those. After I run it for 30 mins and park it. It will leak slowly for an hour or so and form a puddle about 3 inches wide and 12-15 inches long on smooth cement. I will add a pic of the engine casting number. I would like to buy a newer type rope seal if I can figure out which one to get for this engine. The leak appears to come from the passenger side area of the rear main seal. No other leaks from anywhere around the rear of the engine. I also removed and cleaned the crankcase vent tube  and the valve cover had vent holes on it that are free and clear. It seems odd to me it will leak for over 30 minutes after it’s parked. Any help would be appreciated.