i'm changing the differential oil in my 84 z28, std differential, a4, 3.73 gears. i'm getting a mixed reaction from the posts i've searched on weather or not i have to add any kind of additive to the valvoline 85w non synthetic gear oil i got to change it with. its not posi, so do i have to add any additive being that mine is NOT a posi rear end? thanks.

 

No, the additive is for the discs that is in the posi differential. You are fine with just you're synthetic oil.

 

i bought non synthetic oil. just regular 85w valvoline gear oil. does that make any difference?

 

No.