Bart and Larry D
Thanks for your responses.
Bart - I have had no luck in removing the Triangle.
I assume I work on the inside one. Which side do I try to lift out - apex or window or windshield side ?. The MBZ CD just covers removal of a pre existing mirror
but implies you are correct, door panel doesn't have to come off.
Larry D -- I haven't bought the mirror, since I've yet to establish that I have the smarts to install it myself. The parts section of this site sells a used one for a little over $200.
Still looking, and I will get one; don't want daughter shot for cutting off someone (a BMW?)in her blind spot!
'75 240D 300000 miles