Thanks very much for taking the time to type all that.
I did pull it down, and there was a sign of impact on the probe.
As it goes, the spare I had on hand was the new type. I bolted it up, set the nozzle height (which was exactly the same as the old one), and it's away and printing.
I'm very much out of my depth with the programming on this thing, but my wiring and build has been solid, as this thing's been an absolute workhorse for almost 3 years.
I actually bought 2 sets of gear (I have 3 more dead Zortrax's sitting there), and have never bothered fitting up the second.
I'm going to have to bite the bullet and try and update the firmware though I guess...take a deep breath David! We know how that's gone every time, lol.