On Tue, 22 May 2018 17:35:04 +0100, Patrick O'Callaghan wrote: [....]
Never mind. I have actually brought it up before now (can't be bothered to track down the post though it's probably on the KDE list) but no-one else reacted so it doesn't appear to be common.
Fwiw, the pan item in the latest dnf upgrade worked the trick : PC #1 and PC #3 (but, oddly, not PC #2) now boot to their accustomed GUI, and from there launch Pan. All this *without* (at least yet) replacing LightDM.
I guess that makes me mathematically 2/3 of a happy camper; but in practice it's a lot more, inasmuch I now I have not only Pan back, but also a working backup for PC #1.
Many, many thanks! Blessed be the developers!