Look on the back side of the diff housing. Near the top, maybe 3/4 of the way there should be a 14mm allen plug, that's the fill plug. The drain plug should look the same and be situated on the bottom flat of the housing.
Let me know if you find them.
'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.