OK, I took a punt and bought it back, as the vendor had reduced the price to £400. As I sold it to him for £650, it seemed a good deal, if what he described as damage was just lack of knowledge. I had contacted him, and he had told me that he hadn't done anything, it had just stopped working.
What he seems to have done is to try using beeswax on the wheel instead of rosin, not suprisngly this did not work. The wheel may have got a wet spot on it at some time as well, as there was a swelling on it. After application of a cabinet scraper, this sorted that problem.
When I originally sold it, I had very little knowledge on how to maintain a hurdy-gurdy, and it still played, albeit not brilliantly. Having now had 5 other instruments of varying ages and styles, I have obviously soaked up a lot of information, as within an hour, it played better than when I had it originally.
Therefore I got a playable symphony for £400, although I had previously lost £150 on it. It is not the best instrument in the world, but it was the one that got me into hurdy-gurdy playing, and as such, holds some sentimental value for me.
By the way, I would not recommend anyone buying one of these, as I have seen others that were virtually unplayable. I was obviously lucky in the first place.