I’m not familiar with the inner parts/path of the tow mirrors tho I can’t imagine it’s much different in there. All the wiring goes thru the arm from the glass and down thru a cylinder shaped piece that is also the pivot point for the mirror. On the regular ones there are a couple panels you can pop out to get access. But it’s still pretty tight.
There’s a vid on YouTube about completely disassembling the arms to replace those gears (for the power fold) but it’s for the regular mirrors. Might reveal some similarities? Pretty involved, but worth a look… found it: