CrazyCarl wrote:
You'll need to get a screw extractor. It's a fairly common problem that screw and bolt heads snap off. One detail that might make this situation a huge headache...which side mirror did you break off? I believe the left side is reverse threaded, which means you might just have to drill it out completely and retap the hole.
None of the bikes were left hand thread left hand mirrors until about 2012 or so, and then it started to randomly happen with various models. Yamaha did it since the beginning with the right mirror, but most of the companies have never done it. I'm not sure what was the logic behind Piaggio switching.