Not sure if this will help or not:
The 126 has a plug on the door jamb, remove it and pull a single phillips head screw. Then slide the handle assembly forward to disengage the mechanism and lift out.
Take a look on the "M" and see if there is a plastic plug in line with the handle, then take a looksee under the plug.
'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.