I need some advise. My TR-250 has always had this problem since I owned it in 1975. The transmission will pop out of 3rd gear if I don't keep my hand on the shifter. I had a new transmission rebuilt kit put in, but it did not fix my problem. I talked with the tech guys at Rimmer Bros. in England and they said it could be the "detent balls and spring" on the selector shaft. Would like to get some good advise on this issue. Thanks and Happy Fathers day to all.