Just came back from the mechanic, he was almost positive that it is an O-ring from the oil filter housing that's dried and cracked. He said that he had to fix dozens of 7 series with the same issue. All said and done $300 (mostly labor, since the O-ring itself only costs about u$s 6.50. That is with the filter housing NOT being cracked though...
I asked him about the one Oring from behind the alternator and he said it was all the same assembly on the drivers' side of the engine.
And you're probably right, it's unlikely that BMW would use different quality for different exporting destinations. But I tell you, I test rode a Volvo sedan (dont remember the model.. S40?) with 90k miles and it felt like a bag of screws in a blender and it smelled like grandma's living room :P There's an example of fidelity over mileage!
I recall back in Argentina cars with 200k Kms. and going smooth like butter! (overpriced too! ha)