I had this problem, but a have fixed it. I had to change some parts in the engine.The drive gear for 2 nd gear, selector fork both of them.I also changed the Gearchange drum because it had some damage. Since then the gear have been working perfectly. I took ou the engine, turned it upside down and replaced the parts from there. It was not necessary to take the engine appart. Just dismantle the bottom part, and you can see what has to be done. I used the Owners workshop Manual , asked around and got some ideas and then found out how to do it when the engine was out upside down.Now I have problem with the petrol taps, I hope I can get som new ones. I have tried to change the caskets but it did not help. I think they are worn out.