Did no one answer you? My local Hanger clinic is fabulous. They have recalibrated, checked, replaced defective electrodes (yes, you get some) all at no charge. I haven't had to repair anything. I have flown several times with it and never had a problem. Since I use a wheelchair at the airport, I go through a special door and then get checked manually. They don't pay any attention to it.
How are you doing with it?