If anyone has this problem of the stud holding the muffler to the flange twisting off, I had this problem and I have a fix. It requires a hack saw blade only because there is no room to use a hacksaw in there. Using just the blade, take your time and cut the remaining bolt off if it protrudes beyond the surface of the flange. It is a soft bolt and taking your time with breaks to rest your hand, it takes about 20 to 25 minutes to cut it off. Next it is necessary to drill out the remaining stud. To do so and get it on center, remount the muffler and if you have one stud intact, tighten the bolt to pull the muffler flange surface up tight to the exhaust pipe flange. This is necessary so you can have a drill guide to place the drill bit in the center of the stud. Now find a drill bit that fully fills the bolt hole in the muffler flange so it does not move around and permits you to place the drill bit in the center of the broken stud. It is only necessary to drill a good starting hole so you can then remove the muffler and now begin drilling a pilot hole and progress upward to the size that permits you to place a 6mm bolt in the hole where the stud was once in place. After drilling the hole and cleaning up both surfaces of the flange with a file, place a 6mm stainless bolt of sufficient length to attach the muffler. Be sure to use anti-seize compound to prevent having to go through this whole drill (no pun intended) again. I am told an anti-seize compound containing copper is necessary because of the temperature incurred at this joint. I know I could have taken the exhaust pipe off at the connection to the head...but if I had a problem with the aluminum threads adhering to the steel bolts, well I then would have had a much greater problem.