Here is a pic of my differential. It is posi or limited slip or whatever, early 3rd gen 7.5 type 3.73 rear end. I got Lucas high performance 80/90 plus gear oil. The oil says its excellent for use in limited slip differentials and no special additive is needed. I bought a tube of K&W posi rear additive thinking I needed it. Do I need to put this in? I dont want to mess anything up by putting or not putting the additive in.
Thanks

 

If it already has friction modifiers in it than you shouldnt need to use the additive. I bought some redline performance gear oil and it already comes with it so I dont need to add anything.

 

No additive needed, thats a grenade lock anyway, additives dont do much good. I had one in my 85, it lasted maybe a month.