GR6 ETS (AWD Unit) Ball Retaining Ring
This ring is designed to hold the ETS preload balls in place inside the unit. If the clutches inside the unit wear out, the balls will fall out of position and the unit will seize. This will cause serious damage to the ETS unit, and can also break the ETS Output Shaft.
If you are servicing your ETS this shim is cheap insurance to avoid catastrophic failure.
How to install it yourself HERE.
More info as to how it works HERE
Shim is made from 2.5mm thick steel water-jet cut for accuracy, will easily contain the balls, and can save thousands of dollars in unwanted damage if your clutches wear out.