I reread the post it says the nut backed off ,if it backed off on its own how can the threads be that bad usually the threads get wrecked when you take a rusted nut off with an impact Sent from my iPhone using The H.A.M.B. mobile app
I have repaired threads in tight spots using a small triangular file and carefully cleaning the threads up.
My threads are fine. I`d check the threads with a gauge and check the nut to see if it`s the correct one. If you have limited tools, take it back to the shop where you had if fixed in the first place. Exhaust leaks and little kids riding in cars is not a good idea.
induction heater never seen this before doesn’t help with bad threads but would come in handy Sent from my iPhone using The H.A.M.B. mobile app