did you not notice the splines were getting lose or do you just have a heavy foot?

 

I had a flat spot in the spline that introduced itself to me in Albuquerque on the way to Sturgis and no I didn't notice any slop until I tried to downshift and the shifter was laying flat on the floor board.

 

If you haven't yet, check the rear arm on the shaft that goes into the transmission. Those have been loose on every machine I've checked. Tighten now, avoid a big job later. Remember the caution in the manual, using excessive force on the shift mechanism will cause damage.

 

Vice Grips worked for me many years ago on an old Honda 350.
Rounded jaw Vice Grips. Remember it like it was yesterday.
Prevention is make sure the shifter STAYS tight.