he replaced the factory bolts with a nylon lock nut and a lock washer...same problem. I think the problem won't be resolved until he directs the exhaust away from the bolts or goes with the cotter pin method.
You can also double nut it. That is after you get it tight put another nut on there and that will act as a jam nut. If that don't work you can do the extreme and tack weld it. /forums/images/graemlins/smile.gif
Tony