In some of my latest Setups you may saw the following: Diff Washers = SS / Small Shim
I took some photos for you to show whats behind this "Small Shim" comment.

Actually I prefer to replace the WA03 washer in the GD2B Gear Diff by an smaller outer diameter size shim, to allow the silicon oil flow behind the big G08 Bevel Gear.
The WA03 shim has an outer diameter from 15.5mm which cover the backside of G08 fully and nearly "seal" the space between Diff Case and Shim/Gear.
By using the SH5X7X0.3 with an outer diameter from 7mm the silicon oil can flow between the Diff case and the Gear.
(Both shims are 0.3mm thick btw)

During the small shim use, the stiffness of the diff, for example build with 5.000cst oil, will be softer than usually.
This is during different friction between Diff Case and Gear.
It means, if you want to run a Diff with small shim, which should have same stiffness than the std. build diff with 3.000cst, you should put in 5.000cst oil.

The advantage of this "Mod" is a more consistent Gear Diff during the runtime of a heat, which results in "less drop" of laptimes toward the end of your run.

This Mod is also tested and used by most of the the Team Awesomatix Factory Drivers like Freddy S├╝dhoff, Lucas Urbain, Loic Jasmin, Marcel Geiger, Olivier Bultynck, Thimo Weissbauer.

The correct size Shim for this mod can be found here: http://shop.awesomatix.com/index.php?productID=1070

Source:

M. Machler