My folks have an old honda 350 4x4 that is stuck in gear. We have heard that it is because the shift fork bends on thes

 

Sounds like something broke...j/k

There is no way of knowing what caused it to lock until you tear into it.

Don't eliminate drive train binding as the cause either. Check the U-joints and drive shafts. If they binded while in operation, it would cause it not to shift until there is no resistance.