Finally got to the job. Very easy. Backing in to the garage, I caught the mirror on the door frame. The back of the unit, the black curved shell, busted/popped off. It was still intact, though there were a few immediately unrecognizable pieces of plastic on the ground. I thought it was a seperate part, but when I called the dealer, I was told it wasnt- "Oh no, you cant fix those, you have to replace the whole thing" for $150. Ah, f___ that.
I took it off and got it inside so it would warm up. On closer inspection, it was completely intact except for these pieces. I mated the pieces to where they were from (the uneven breaks on pieces and shell matched). They lined up close enough that a liquid instant super glue worked. Now I had two, square, upside down 'U' shaped structures on the inside of the shell. Around the edge of the shell, there were small indentations about 1"-2" apart and tiny male 'nubs' on the other side of the seam where the 2 halves meet. Since I couldnt see inside when I put the two halves together (believe me I tried-small gooseneck LEDs and dentists mirror) I didnt know exactly how everything lined up and met. So I needed a glue that wasnt water thin like the super glue, something thick that would bridge any small gaps. On the dry run I realized the 'U's were the 'female' side of a hook assembly that partially held the two halves together at the outboard vertical edge of the mirror. I used JB Weld, just dabbed a tiny bit at each of the indentations. It all lined up perfectly. I wrapped 3 huge rubber band around the whole thing and drove around without a passenger side mirror...
...24 hours later- like new, impossible to tell it ever happened. Put that $150 to better use.