I tried fitting a new one (India made I am guessing) and the center hole was a little to big and the the gear would not stay centered on the clutch. So went back to the original one and all is still OK.
I looked at my NOS solid gear, fibre with steel centre and it is the same width as the later clutch type, being 1/2". I would rather fit the clutch type but if all else fails then in it will go, at least the bike will be running again. I did see Indian ones on Ebay and wondered about them because they are not really that cheap especially if inferior. I will take Ian's experience and advice and avoid them. Still got a couple of irons in the fire so a new genuine or UK manufacture might turn up.
