I noticed some play when turning the clutch (about 8mm on clutch outer drum).
On further investigation I found the nut on the end of the cylinder shaft was slightly loose so tighten it. It ran OK for a couple of weeks then it happened again.
I just re-checked the shaft/key slot and it is quite badly worn (I assume through many years of cutting stones!).
The key seems OK as does the chain wheel but when the key is in the slot there is about a 1 to 1.5 mm along the slot!
Other than try and find another cylinder is there any way to salvage the present one!?