Try doing a search for a thread titled "look what Mobil One did to my rear end" or might have been differential, can't remember who posted it though. Has pictures of an extremely clean differential housing after something like 1K miles. I'd imagine it would clean the innerds of a crankcase as well.
'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.