PABLO 332 - You are not causing offence but:
For example, you imply that there is more load on the shaft due to the higher torques through the box as a likely cause to the failure but this is not consistant with 8 years of trouble free operation!!
Like I said, how do you know the shaft suffers greater lateral loads??? My understanding, and I am far from a design engineer, is that this type of pinion/crown arrangement is self engaging and expressly designed to reduce the effect you describe...but like I said I am not an engineer.
Facts only are needed now.
DB