Just received a letter from Bose re replacing the headset cord. The good news is that Bose will do this at no charge. The bad news is that one will be required to disassemble the headset (remove the cord - tools required) and send it off to Bose before they will send the replacement, so you will not have the use of the headset until Bose sends the new cord. Not a big deal if turnaround is quick, but not the most convenient approach. See
Bose A20 Aviation Headset Customer Update for full details.