Thanks Jimmythree
The watch is genuine, but I have not used for 20 years and I just started wearing it again. A quick dip in a swimming pool and that was the end of it.
I see that it is worth around $3K but I would not rush out and buy one, hence the idea with the cheaper repair. To get hold of an original Hublot branded movement would be $1,000 plus, but an unbranded ETA movement is $300. Also the rubber strap has gone a bit hard and I see cracks appearing which means that it is coming to the end of it's life as well. That is why I would swap the rotor and no one would be any wiser, not that I am planning to sell the watch.