Has the selector been jumping or like bouncing while trying to change gear. I had worn dog gears on my YZF yamah which caused the selector to jump in and out (terrible feeling) it bent the selector arm (small lug on the shaft) I fixed it a few times till it stranded me and I had to fix it (was stuck in neutral) replaced second and sixth gear and selector arm, forks and drum. Was a big job had to pull the whole engine apart - pistons off the rods etc justto crack the case.