I am going to replace the fluid in my rear diff.
For the clutch lsd rear diff on the S4 turbo 2 what is reccomended. This car will see heavy track abuse, I beleive besides 75W-90 there might be a LSD additive I need.

So let me know what I should run!

 

75w90 will work fine. Almost any of the major brands will work well but you will have to add some LSD additive to them all for the clutches on the LSD to work right.

 

so if I go to autozone I will find a LSD additive that I can pour in with the diff fluid?

 

ya get a synthetic additive if you are going to run a synthetic fluid.

I run 75w90 redline GL4 gear oil with Redline LSD additive.