02 yz125 gearbox question

[skiddo]

My son rides a 2002 yz125 which was laid up over the winter,we started her up ran the bike only to find that everytime 4th gear was selected the engine revs like its in neutral and the clutch was very springy/tight.I stripped the motor down and split the motor to look at the gearbox,what i found was that a bearing retainer on the main axle had broken which allowed the axle to move over towards the ignition side were the axle is supported by a needle roller bearing.Now the bad bit,apart from the broken bearing retainer the main axle on the ignition side was reamed (just up from the circlip) also the needle roller bearing was damaged by the main axle being allowed to move too far into the bearing.I replaced the bearing on the main axle,the needle roller bearing and the bearing retainer,we started the bike and it ran good apart from a rather springy/tight clutch (again) so next day up to the track and with in 5 to 10 minutes the problem reoccured.Stripped again and yes the same problem exactly again !
I am now at my wits end as to why this happened in the first place,i just cant figure out what caused it and i am asking now can anyone tell me why this happened ? i believe the second time it happened was due to the fact that i think i should have replaced the main axle(or main gearbox shaft) which when it moves over pulls the clutch basket putting pressure on it and making for a real springy clutch lever.Please can someone help me on this as i am going to buy a new main gearbox axle,bearings and retainer but dont want to see my son gutted again.
Yours. Robert Graham
p.s. i will try to get a diagram up on http://www.skiddo.net

 

[skiddo]

I have just uplaoded some pics of the gearbox to
http://www.skiddo.net/imagesgearbox.html