07 Differential Fluid, how much LS Additive?

I have a 2007 AT. I understand that when changing my rear diff fluid I need to add “LS additive”. How much do I add? I can easily find how much oil to add, but nowhere can I find further details on this LS Additive stuff. Also can someone link my to the plug and washer replacements. Thanks in advance.

 

LS additive comes in a 3 or 4 oz bottle, add the whole thing with gear oil change.

Then find a lot to do 10 figure eights in both directions.