Buying a replacement anything is a good way to make the original work again, and that's what happened here.
I was looking at the hands on the clock, which were slightly bent, and in the process presseed on the axle in the middle to which they all connect. This caused it ro burst back into life. There must have been a loose wire or something.
The new clock makes a slight whirring noise as it goes round, so I stuck with the now-functioning old one. The new one is under the TV, where no-one can hear it, and it's more visible than the carriage clock also we have there.
I guess it'll have to be moved when the grandchild gets old enough to self-propel, but for the moment it's doing a splendid job.
Yes, I know the two clocks in the picture aren't exactly synchronised, but so long as neither of them is slow I'm OK with that.