My 528e had a minor oil leak when I bought it with 150k miles. It used a qt every 1500 miles. It was a porous spot on the headgasket, a common problem in that engine. I put another 200k on the car without doing anything but adding oil as needed and changing it evry 4-5k. Cheap oil and filters. The oil worked its way back on the frame rails and rust proofed them.