It's fairly well documented that the pre 07's have a locking lever that contacts the shift drum that is faulty. Save yourself from some headaches buy laying your bike on the right side and take off the clutch cover off.
In the photo below... if the forward lever contacting your shift drum has a ball bearing on the tip it needs to be changed, the outer race breaks and you end up with large shrapnel in you oil.
Here's mine with only the inner race is left (very undesirable), in 08 they upgraded the part to have a bushing instead of a bearing. The new part is $12 and well worth not having to split the cases and sit out the best snow of the winter.
In the photo below... if the forward lever contacting your shift drum has a ball bearing on the tip it needs to be changed, the outer race breaks and you end up with large shrapnel in you oil.
Here's mine with only the inner race is left (very undesirable), in 08 they upgraded the part to have a bushing instead of a bearing. The new part is $12 and well worth not having to split the cases and sit out the best snow of the winter.