You'll need to get an "easy out" if the stud is broken off flush. I have replaced the factory studs with pieces of "all thread" that you can get at most hardware stores. Just cut them to size and turn them in. I have been having problems with the studs stripping out of the block/cylinder on mine. Be careful with how much torque you use!
If it can't be broken I'll find a way!
I'm not lost, I'm exploring!