My 2011 YZ450F has around 50 hours on it now. Yesterday 4th gear started to pop out. Came on a straight 4th gear pinned and it just poped out. Anyone else with this problem ? I´m very kind to my gearbox and mostly even use the clutch. Never kicks in gears and do any hard stuff to the gearbox. Changes oil every 2-3 hours. Had never had gearboxproblems on any of my Hondas. Is this a common Yamaha problem ?