Michael,
I am also surprised that you get away with less springs in your S6 clutch - especially as you are using a 'Ferodo' type lining. On the postwar models, Douglas used Ferodo but reverted to cork linings for the higher powered 'Plus' models to prevent clutch slip. Also, the original S6 clutch plate only has the corks protruding about 40 thou, so I wouldn't have thought there was enough room for a 'Ferodo' lining without reducing the thickness of the plate. If this has not been done, then maybe it has affected the operating geometry of the clutch release.
On the subject of the ethanol - we are all suffering from the effects of the modern brew that masquerades as petrol. If left in a carburettor to evaporate, it usually leaves a sticky residue that either blocks or severely restricts any jets, and causes slides to stick. This problem can be exaggerated on machines like the S6 due to the close proximity of both the hot exhaust and timing chest increasing the evaporation rate - the S6 is a big old lump that takes ages to cool! Whatever machine I am using, I make a point of turning off the fuel and leaving the engine running until it empties the carb before putting the bike away - this seems to have got over that problem.
Regards,
Eddie.