OK, taking a lot of suggestions here, that is good. Thank you.
Getting into engineering mode in the good Zumo will allow it to show up in updater. So that is a positive sign.
Still no joy with the bad unit. With the magnet, going through the multiple ways to get into pre-boot, still can't get it to show up in updater.
And with the multiple ways, I can't even get re-boot to show on the good Zumo.
Sorry to be such a pain!