Stang, I recently noticed my countershaft had alot of countertclockwise/ clockwise play on my 250. Switched to a newer sprocket and most was gone. The notches on the inside had become worn before the teeth on the outside. Weird to me. I think those spacers can wear also, and some sprockets are thinner than others. Somethings going on if you can get a washer behind the sprocket.
Good, I have a yz 125 that likes to stick in gear. It always gets into third, and second some how. You can pull the clutch cover and fix it. I have fixed mine several times with the shifter. easiest way was to ride it in the gear its stuck in, and shift up a couple times, then back down, but it doesn't happen that easy. Most likely the parts inside are in a bind in the open or shifting position. Not sure of the right names of parts or terms, but, if you pull the cover and start playing with it, either the 4 pin'd barrel will be caught half way in a cycle, or the flat metal slider with the springs, is stuck extended, or both. It could be something internal, of course, lets hope not. Its likely something simple.