Have you had the car detailed since you purchased it? Maybe somewhere along the way some engine dressing has been sprayed under the hood and the sand and dust is sticking to the dressing. Some of the dressings I've seen have an oily film. Have you ever had a belt chirp that someone's tried to identify? I suppose it could be belt dressing as well, although as new as the car is I'd hope that's not the case.
I'd suggest you clean it off and see if it returns. I agree that it's probably not a leak from the battery.
-Rod