[cfelton]

Try PB Blaster, I've had really good luck with it. If all else fails, you can weld a small washer flat down to the leftover stud then weld a nut flat down to the washer. While its hot work it back and forth with light pressure until it gives up. If you can get hold of stud rods to weld the washer and nut onto the stud they really work great. Let us know how it goes! We remove broken off rusted bolts at work like this all the time.