Stuck starter motor

[Mad Mac]

Thanks everyone,
I understand from your replies that the "spindle" (the small cog) and the ring gear should not have grease on them,but should the "helix" (the worm thing) have grease on it? Mine has worked well for more than 20 years with graphite grease on it (see photos in post #16 above) and only very recently has it started to "stick". So, am I right in concluding that grease on the helix cannot be the cause of the problem? I guess I really want to understand cause and effect here.