Here a pair of taper roller bearings (14) spaced apart within the removable pinion housing, support the pinion shaft. From what I can see the Quaife bevel box employs similar pinion support to that of the proven Guzzi design, so I don't think you can lay the blame there.
Hmmmm ... your correct. Looks like a bit the same as the Quaife unit but somewhere need to be a difference because so far as I know the Guzzi units don't scream. Does someone know if the heart lines of the pinion and crown wheel are in the same line in the Qauife unit? Looks that in the BMW and Guzzi the pinion is lower as the crown wheel. But I only can see this from the drawing / picture so perhaps I'm wrong.