Halfnut is pointing in a good direction. Cut off the bad section and turn a short length of the OD to form a pilot. Turn a new section with the threads and with a female counter bore to match the pilot diameter and then braze the joint. The pilot serves as a fixturing feature to insure alignment and also makes for a lap joint for brazing as opposed to a butt braze joint. Just my thoughts. As for inserts there is most likely not enough material to put one in and besides the reverse loading will cause it to come loose, be it a wire insert or solid insert. Also the L/D of the insert would be too short.
When on the hunt, a broken part is better than no part at all.