limited slip?
limited slip? I have a 2001 ws6. Do I need the limited slip additive in my diff? I believe it takes 75w90. Got 25,000 miles and have changed it twice, just without the limited slip fluid. I think 75w90 is synthetic, with the additive in it. Please help me out here. 
I think 2001's have a Torsen posi which doesn't need the additive, but it won't hurt anything. The Torsen is a gear driven posi, which doesn't require a friction modifier like the Auburn, which is a clutch posi. The Auburn was only used I believe in 98 and some 99's.
There was a GM TSB to add the friction modifyer to the torsen diffs if your diff was making a "rusty screw" noise. It's not needed and the rusty screw noise (as they called it) won't hurt anything either, they added the additive to remove the irritating noise (keep customers happy). So, as stated, you don't need it and under some conditions GM added it to quiet down a noise.
