OK, I finally made a little progress. First I emailed Winnebago and the reply was to call Dodge service at 800.992.1997. They said they had NO info and I had to call the dealership. So I call my local Dodge dealer and they don't sell OR service Sprinters and I should call the closest Sprinter Dealer which is Browning in Norco, CA. 951.272.3110.
After some phone monkey business, I got to talk to a tech. Here's how to open up the outside mirror.
1. Adjust the mirror to its uppermost position.
2. Then pry/twist the mirror in the direction away from the door (to the left on the driver's side).
3. The mirror pops off.
I did that and now I can see what I have to do, and I didn't break anything (yet).
Pressing it back on took a couple of careful minutes, but it snaps back on. There is a pivot in the middle which has some grease, and there are 4 little plungers that move the mirror itself.