Aerosol duster & heat to remove broken bolts.
Plan B:
Get a can of aerosol keyboard duster: notice that when you turn the can upside down and spray, it puts out a stream of very cold gas. We are going to use that to our advantage.
Remove the bracket and apply heat to the area around the offending bolt using a propane torch or even better, put it in the oven at 400 degrees. If you use the oven method, make sure that your wife isn’t around. To measure the temperature of the part, you can rub a stick of high temperature melt hot glue on the part near the bolt. If the glues melts, the part is hot enough to work with. The high temperature hot glue melt somewhere in the range of 375°-425°, which is right in the range that the part needs to be for best results.
Get a pair of Visegrip pliers handy, you are going to need then. Put the plastic straw on the aerosol duster, you want to spray a narrow, concentrated stream of the cold gas. Once the bracket around the bolt is good and hot, turn the can of aerosol keyboard duster upside down and spray the bolt on both sides for about 10 seconds each side. The aluminum expands multiple times more than steel does and when you spray the bolt, it shrinks a bit. This is because of the mass of the aluminum is much greater than the bolt. That will often give you just enough slack to twist the bolt out.
Note that ordinary hot melt glue melts at about 250°, which is a little too cool for what needs to be done.
