525i wagon
Considering purchase of at 260k miles. All the noted usual parts (on line) I have read about, have been repaired. All vehicle repair tickets from day one. Oil leak (engine) at front passenger side. Lands on AC and can see approx 2 thimbles worth on top of AC. Not reaching wheel well or eating belts. Owner says it's been doing it for last 40k (the length of time he has had car) with no increase in leak. Tail pipe is medium to dark black but no signs of water. 80% of driving is in town. Owner seems very knowlegeable and competent and has done all repairs during last 40k. Car shows lifetime excellent maintence. Owner does not know what problem is. Covers do not allow observation of possible sources. No water in oil, and oil is 2k old, and nothing in coolant. What is the most likely problem and fix, and what is the worst possible?