Dude,
Have been dealing with the same thing....check my posts.
Tried something today and I am pretty sure it is a band-aid that will work for me as long as I have this bike.
I too have the spinning and no engage of the starter. Now the fix!???
I tried to start it today and got the spinny, then I put the bike in first gear and pushed the bike forward until the I met resistance (trying to push the bike in gear = dragging the rear tire) then tried to start it again normally and boom...full starter engagement! I will continue to try this and see if I am on to something or if it was a coincidence!
G