Usually you do get some sort of mix.
I'm not sure what the MB head gaskets look like though. I know the Detroit Diesels I used to work on had multiple seals rather than one piece. They had black o-rings for oil passages, red for water passages, steel rings on top of the liners and one big old o-ring around the perimeter of the head. Depending on the path of least resistance, the leak could vent to atmosphere without corrupting the oil or water passages, but with a single piece gasket that seems less likely.
My money is still on a head gasket and valves.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.