Getting the windlass (a Simpson Lawrence Hyspeed) off looked like being the easy part. My problem was that the gypsy wheel had become ceased against the clutch cone and wouldn't slack off - hence not possible to surge chain through the windlass, only hand over hand which looked dodgy to say the least. (Those of you with electric windlass stop reading now - you will need all your resources to save up for an extra battery...)
On the bench, the big problem was how to brake the shaft in order to get enought purchase on the clutch nut to unscrew. Fortunately my new best friend at SLSpares (http://www.slspares.co.uk/) was not phased by this. On his suggestion I led a short length of chain over the gypsy wheel and secured between / under the platforms of a workmate style bench to which I had clamped the body of the windlass. Using my improvised handle and a bit of BFandI, a few moments later the gypsy was free and I had a fully functioning windlass again !
It seemed a shame to stop there, so a bit more maintenace will be undertaken, but it does seem that one of the big culprits was the lack of an O ring seal on the shaft under the gyspsy wheel. It was also quite gratifying to find that the grease nipple, although quite badly corroded, was quite easy to remove - up for replacement though in any case.
