It take 8 quarts (2 gallons) to fill the crankcase. Have you changed the fuel filter and air filter? Might help with the surge. You'll be hard pressed to find parts for the 4.5 at the local "parts store". They don't even have the air filter, You might find an oil filter, but I would only use the local parts store filter long enough to get a quality filter (Heingst or Mann).
Most everything you need for your car can be had right here at PartsShop and FastLane, and at good prices.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.