I share your pain,the flange hole closest to the engine needs to be ground a bit because the weld bead is to close to the screw hole and will not allow the screw to tighten flush on the flange.I found out the hard way after mounting once then seeing the problem.My exhaust system from breathles recently fell apart at the inlet side of the muffler ,I had to remove it and weld every weld I could see on the muffler and barckets because several welds were starting to crack.they are very poor welds,if you still have it off the car,you may want to reweld every weld you can see on the unit