Ive recently been having problems changing gear. Usually hitting a false neutral but the when out riding a few days ago the bike made a horrible crunching sound and the engine locked up and the gear lever wouldnt move. I managed to unjam it by kicking the gear lever. When i got it home i started it on the stand without any problems but when clicked into 4th it would lock up again? Ive got the gearbox apart and cant see any teeth missing but theres a few chips and marks on a few of the gears and one of the selector forks is heavily worn. what could cause the engine to lock up like that? Also would i be able to fit an 07 transmission (gears & shafts & selector forks) in my 06 gearbox?