The last couple of days I've been doing a load of research on the exterior mirror, on the driver's side.
Around town a used one goes for $550. With no guarantee, so I've passed on that one. Using Google for more information, I ran into Bimmerfest and started digging. In the BMW Forums, BMW model Discussion, X Series I found some rather interesting information. I started at the beginning and so far have read 69 Pages. Good stuff.
In the MBW Owner's Manual they describe Button #3 for use in setting the mirrors when going through a car wash but they don't describe how to use it to reset a wobbly mirror, that won't stay locked in the extended position.
I started the vehicle. Pressed the button several times and then hit pisition 1 on the side of the seat and there it was. All tight again.
That part I found on your forum. You just might have saved me $700. Plus.