[Golsovia]

On a secondary that old you'll undoubtedly need to get the clutch apart to maintain it properly. Turn the sheaves against each other so that neither is in contact with the helix. Press the helix onto the shaft. Kroil works better than anything else I've tried to help it move if it's stuck. A little heat may also work. In either case, once the helix is in, clamp it if it wants to come back out so that you can dress up the end of the shaft (remove the big clip), polish the shaft with emory, and pull it apart. Once you're inside you can inspect the parts, find out what's binding and replace whatever needs replacing. They're not that tough to work on unless they're really stuck. Patience is the key if the helix won't move.