Hagerrog, we could help more if we had the ebay item# or link to that, I haven't seen any BMW mirrors that are similar to MB, but the rectangular side lights (running lights on the fender) are the same in several of the MB's and BMW's from the 80's. That is all I know that is similar between these makes (oh yes, some Hirschmann antennas can be interchanged between Beemers and Benzs if you cut the plug and rewire it).

BTW, what year car do you have?
115's vary according to the year, the early chassis (73 and before) used a wing style vent window on the front doors and a chrome mirror on a stem and were left off the 220 and 240's (or made optional?) thus making more profit for Benz.
74-76 chassis have one piece of glass on the doors and the mirrors are considerably different, being like those used on 123's with internal position adjustment handles and so on.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!