I just serviced my 2004 450 and cam to the conclusion that the 4th gear (primary shaft) was worn out, verifying the gearbox of two other friends with the same bike, I cam to the conclusion that theirs is also the same or worse! I compared it to the 426 gearbox, which is a lot robuster designed. Why? What is happening. I am not reading anything on this forum about gearbox problems, but it seems (3 cases) that the gearbox (esp 4th) is wearing out premature, can anyone with similar experiences confirm this?