Anytime the nuts need to come off any exhaust studs, start spraying or brush on some PB blaster or liquid wrench - 2days ahead of time ( every so often through out the day(s) if possible) let it soak at least overnight. Turn nut slightly back and forth untill it loosens, spray more penetrant and keep working it untill nut comes off. Once this stuff gets in between the nut and the stud you’ll be supprized how easily nut will come off .