I have suffered the "5th gear won't engage" failure on my 05 WR450 that seems to be fairly common on WRs that have done lots of road running. My bike has done 12,000km - I suspect most of it on the road in 5th gear (I've only owned it for the last 2,000km or so). I'm getting it fixed (a couple of gears, a selector and a couple of bearings), but I'm wondering if a later model might have a more robust transmission for road work. For example, a lot of engine changes were made between 06 and 07 and I wonder whether upgrades to the transmission were included. Anyone have any thoughts/info on this?