Oh man, I almost had the same thing happen to me when I was backing out of my garage. The outer edge caught and flexed enough to pop the blue cover away from the black piece. I felt my heart skip a step. Fortunately, the glass didn't crack. But at least you don't have to replace the entire mirror mechanism.

Bummer... check the prices at Fred Beans OEM Car Parts | Performance Car Parts | Fred Beans Parts Doylestown PA

Try EBay if you want to keep it stock. I think it's around $120 on there. Not sure how much the dealership would charge.