I have to go here with martg.
Had all sorts of problems with starter, except the free wheeling.
Changed batteries, wirings etc. Nothing helped.
New starter from demo bike - BANG! Now the bike cranks and starts like a hurricane
The problem seems to be that there really are multiple issues with starting, so also there is no one fix. But trying a digferent starter is also a valid option.
I hope you get it solved, a working starter is nice thing to have in a bad spot...