Just a bit of info for anyone interested. I changed my engine oil to 15/50 w fully syn as my curvey has done 30k miles and I was shortly going to the South of France where it can be Very warm . After a couple of days my clutch started to muck about. I stripped it and found very little oil on the plates. After investigating the workshop manual I spotted a reference to "oil jets" in the lubrication system. I guessed that not enough oil was getting to where it needed to be due to the thicker oil, so I changed back to 10/40 semi-syn and the clutch is now perfect
