For the benefit of someone who might find this post in a search:

Here is what Donnie has to say about W140 side mirror replacement -

http://www.peachparts.com/shopforum/showthread.php?t=66156

This fellow in FL might still be in the mirror rebuilding business -

http://www.peachparts.com/shopforum/showthread.php?t=61429

And yes, someone doing a search would find those other posts too

Sixto
93 300SD