Solution to this mysterious oil leak:

O-ring on oil filter housing was bad, which caused the oil filter housing to loosen over time, which under pressure eventually led to oil just splashing out of the oil filter housing.

Dealer replaced o-ring and did an oil change and steam cleaned engine, however as I'm out of warranty, the thing had to be flat bedded to dealer and all that work ended up in a $300 bill - all because of a crappy o-ring and badly tightened oil filter housing....