I recommend JB Weld. My right mirror got "stressed".... by the ground... NO, I don't want to talk about it- makes me ill to this day.
My point is- the structural piece of aluminum underneath the plastic mirror pieces was cracked- all the way through...yea, she hit pretty hard. As you probably know, these items are sold only as an entire assembly. I took it all apart, JB Welded the top and sides of the bracket one day, and then put a lot on the underside of the bracket the next day. Put it all back together and can't tell the difference- except for the scratches on the underside of the mirror. Although I won't be folding the mirror in anymore. I dont' need to, and it will still fold- I just don't want to needlessly stress the bracket. Good luck.