On the bike I am helping with the splines had worn away so completely that even turning the rear wheel over to move the chain over the sprocket did not produce any noise of feeling of roughness. The remarkable thing to me is that there was no sign of this untill the clutch cable broke. I am guessing the the sprocket was held just enough by the pressure of the large nut to prevent it being loose. My post #40 above has an error in it. Because of my lack of familiarity with the bits I wrote that the splines which took the final drive sprocket showed signs of wear. That was wrong. It was the splines which hold the clutch centre, which seems to only go onto the splines by about 4 mm. Hard to criticise something which has lasted seventy years but it does look as though a longer overlap of the splines would have been better.