[buzzinhalfdozen]

When you have the cover off , by hand engage 3rd gear synchro, to see if it goes fully onto the speed gear could have a thrust washer or some other issue preventing full engagement. I agree a worn fork can cause this should be easy to see, measure the fork pad area then the synchro slot width,should be maybe .060-.100 clearence would be my guess. Also how is the fork attached to rail, could be a sheared pin or set bolt. All guesses but hope you find it. Joe