Is there a way to tighten down the glass of the outer car mirrors?

I can see them flopping up and down, when I am at freeway speeds of around 70 to 80 miles an hour.

I checked the houseing on the drivers side and it is loose, but the mechanic said I will have to replace the whole assembly. I am not convinced that will fix my problem, because the passenger side mirror assembly holds tight and does not move when wiggled with you hand. but the mirror still flops around.

Just want to get opinions before I drop 400 bucks on the drivers side assembly.

besides the flopping at freeway speeds, the mirrors adjust and the assembly folds in and out. the fluttering is just annoying.