I saw conflicting reports on whether the rear diff in my 1998 needed limited-slip additive or not. The 1998 is an Eaton locking diff, I am pretty sure. You're right about the diff being different in later years though - more specific research would be needed to determine what fluid is recommended for the later models. The 1998 was a bit easier because it uses the rear diff from the 960/S90 which had pretty good documentation.

I decided to err on the side of caution and add the limited-slip additive. Amsoil sells their own additive called "Slip-Lock" I think, so that's what I used because I was at the Amsoil dealer already. I'm sure any limited slip additive would have been fine though.

The additive wouldn't hurt a diff that didn't need it, but would be important for one that does. I never really got a firm answer on whether not having the additive would actually cause damage or just create the 'locking chatter' that is common on 4wd systems with locking diffs... again I chose to be cautious and use it.

I followed your tranny fluid thread with interest. Hopefully a small mistake on the trans fluid level was the worst you'll find eh?
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1998 V70 AWD->FWD Turbo 200k+