The following images would most likely be your problem.
I now know the answer I've been looking for and the answer for a few others to why their mirror folds one way but not the other.
TAKE EXTRA CARE PLEASE.
Don't do what I did and break a wire off the small motor. Better to cut the wire off and solder it back. I kept moving it out of my way and it broke. I can fix but will not be easy.
Now looking at the images you will see what is inside the little white dome. Close circuit terminal connectors to only power the mirror so far one way or the other. if one side of the connectors has broken then the mirror will only fold one way. When both are broken they will no longer fold.
