pearlwhitemax

A few months ago after remounting my driver's side outside mirror, I overtightened one of the studs (there are 3 holding it onto the door frame) and half of it broke off. Part of the shaft is still stuck in the hole for the mirror. Is there any way I can get that sucker out so I can put a new 10mm bolt? The glass and assembly shake a little when going over bumps. I also noticed there is a small philips screw on the underside of the mirror outside of the car. Any idea to what that holds? Thanks for any advice.