i would like to add some ideas to welding the bolt out i work at a john deere dealer ship and we have alot of broken bolts and the only way i get them out is weld them out i use a 3/16 stainless steel welding rod because of the high tensile strength its the only stuff i use i get a few nuts one size bigger than the broke off bolt and stryke an arc and build the old bolt up into the nut with out welding the nut to the bolt let it cool a tic and keep doing till bolt is built up to the top of the nut then i burn the newly formed bolt into the nut and then after it cools to a slight glow slowly work the nut and bolt back and forth be gentle and patience is key take your time you will prob break the nut off a few times but all the heeting and cooling will break the rust loose and it winn eventually come out i have never not been able to get a bolt out