Took the old slave-cylinder off from the clutch and got the new one out of it's wax-paper for the first time since it was bought in 1989 and the rubber and piston look spot on. The rubber-hose is also in good nick, but the threads at either end had become a bit rusty and I had to clean them up with a wire-brush. The lever to the clutch-piston looks in good order too, but I suspect it will take more than the hydraulics alone to un-seize the clutch-plate after so many years.
With the clutch now complete along with the brakes I threw the master cylinder back in, which was a bit over zealous, as it had to come straight back off to allow work on the bulkhead. Good job really as a test of the master-cylinder revealed a seriously fluid leak from the clutch side plunger-rubber. It was also full of a grey sludge, so after a swill-out and letting the silicone brake-fluid soak in we left the master-cylinder for the time being in the hope that the fluid will swell the rubbers and create a seal against the leak - if not it'll need a new set of rubbers for £10 or, if were feeling flush, maybe a whole new unit for £109.