Hello! Just got back from the 200 mile trip through the sandy beachers of Sakhalin Island. In the middle of the trip noticed that the bike would not switch into the 5th gear. Stopped the bike, no metal noise from the engine. Stopped the engine, checked the oil level, oil seemed to be OK (no metal dust).... 1-4th gear work just normal, returned home carefully.. Has anyone else had a similar problem? What do you guys think I should start with? I am afraid that I will need to get inside the gear box anyway, but would like to have some opinion before taking the cover off.. Please help!