I would expect aluminum or pot metal, magnesium is too expensive and corrodes readily. If you can get it off, or get at it good enough, you could drill and insert a Heli-Coil.
I'd second the Heli-coil solution. They work good. We put them in all four threaded holes of the windshield mount.
Former Happy Spyder Owner
Just decided it was time to move onto other things.