Oh yeah, let me add that if in doubt about what kind of differential you have, take a good look at it when you have the cover off for changing the oil.
Then look it up online if you don't know what you're looking at. Also, I think the SS models got the Torsen before 99, another reason to double check.

 

I see. I must have gotten lucky then. I'm pretty certain that the Lucas I used was synthetic, but I'm not a 100% sure so I'll check today when I'm at work. I also didn't use the additive because according to Lucas, it wasn't needed and I figured I'd give it a shot and haven't had any noises yet so I'm thinking they really don't require it.