To find the center on the MB boxes I have seen, there is a cap (which looks like a bolt) on the body of the box. remove it and look inside, as you turn the gear, the centering hole will line up with the bolt hole - when aligned, the gear is centered.
'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.