I finally cleaned up my 2.2 190d engine compartment enough to find that my oil leak is from the head gasket; the gasket appears broken around the front of the chain galley. The leak is very noticeable but frequent checking of oil level will contain the problem.

There MIGHT be a small skip in the engine at slow idle, but other than that the gasket seems to be performing its task. No white smoke, no oil in the coolant. There is blowby at the valve cover as well.

So the question is-- drive it some more or fix now?