Had a minor revelation today. A few months ago, when the driver's door was opened up to replace the window regulator, a small black plastic piece with a circular indentation fell out from inside. I had no idea what it was, until someone posted a photo of their mirror switch... it was the top part of the little "joystick" that adjusts the mirrors. I had no idea there was anything like that on it. Snapped it back into place, job done.