I've had a couple times in the last month when I found a very small amount of oil (a few drops at most) under my motor. One time it was on the port side, another it was on the starboard side. In between those two occurrences, there were a couple times I motored and there was no oil leak apparent, including a 6 hour day of motoring with no oil drops observed. But the very next day I motored for another 6 hours (with some heeling during a couple 30 kt gusts) and found a couple drops of oil.
The two times I found oil I had motorsailed and had some heeling in the direction consistent with which side I found the oil. My guess is that there is a slow weeping through a seal somewhere which accumulates somewhere on the fins and other horizontal elements, and when the boat heels it falls off on the low side of the engine. It's also possible that the weeping of oil only occurs when the motor runs while the boat is heeling.
A couple of other notes: I have occasionally found tiny amount of oil on the engine housing this season. While I don't remember exact location, I do believe it was relatively high up on the motor. Also, I did have some water leakage from my Sherwood raw water pump in May which led me to have it rebuilt and to replace the raw water hose back to the HX. I did replace the flange gasket with the water pump. I've inspected the edge of the oil pan flange and noticed a tiny amount of corrosion around the very edge, but no signs that it's any more than superficial, and only about an inch long in one spot. (I'll recheck this next time I go to the boat.) Also, frequent checks of the dipstick verify that there is no measurable loss of oil. It's always at the top line on the stick.
I'd be interested in your suggestions on how to diagnose and locate the source of this small leak. Are there flange bolts I should tighten somewhere? I think it's overkill to remove/replace the oil pan at this point. Would prefer to eliminate other problems first.
The boat is now hauled out. I'll be changing the oil and winterizing in the next couple of days, so may not get much diagnosis done. I'll try to take a few pictures if I see anything interesting. I expect that running the motor for 20 minutes without any load (to heat up the oil) isn't going to put enough stress on it to see any leakage. Also there won't be any heeling with the boat on the stands (there better not be!!!).