Drill out the center of the broken bolt. Get an EZ-Out tool from a tool source. Try to start with a drill bit that is about 1/4 the total size of the bolt. gently tap the EZ-Out in before turning it to make sure the tool "bites" into the metal.
Follow the instructions on the EZ-Out package. If it won't budge try a larger set up ( larger drill bit and larger EZ-Out) Try WD40 or something to loosen the crud around the bolt.
If this doesn't work try some heat right at the bolt before twisting it out with the EZ-Out.
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)