the factory spacer can continue to crush under excessive load, when this happens it changes the preload and back-lash and will cause premature wear and ultimately failure of the gearset.
When fitting a front diff lock a common upgrade is to fit a solid spacer kit to avoid this from being able to happen.
These spacers are Australian made and come with a selection of shims for refinement.
If the correct adjustment can't be achieved with the shims provided, additional shims can be purchased, or the Spacer itself may need to be lapped in.