Hello again all, thought I'd update the situation.
Put another 60 miles on it and, if anything, it was worse: I was accelerating away from some lights and changed from 10 to 11, not under very high pressure, when the gears slipped... it could have been soooooo nasty but my loss of control somehow ended with me mounting the pavement and, incredibly, staying on the bike! I'll put it down to the Pace forks and badly laid kerbstones.
Anyway, I was very shaken and a little reluctant to stand on the pedals again so I pootled along like a vintage shopper. It was quite a relaxed ride actually!
I emailed a detailed saga to Rohloff who replied, at about 5am, asking me, if possible, to send them the wheel. I had asked them if they thought an oil change would solve it, but they were quite keen to have the hub back. Hmmm...
It has now been duly posted, so let's see what those wizards can make of it this time 'round.
I want it back: it was fun while I had it!