When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Most GL-5 gear oils now contain the friction modifiers suitable for use with factory type clutch-type limited slip differentials and for most of these LSD no additional friction modifiers are required. Remember that too much as well as too little of these friction modifier additives are a bad thing. You should be fine with the Mobil 1 75w-90 fluid that you bought in a stock differential or any other high quality synthetic GL-5 fluid from say Redline, Amsoil, Royal Purple or GM.
Now if you have a differential that was setup by someone in the aftermarket like say Rick at RTK, then I would follow whatever they recommend that you to use due to their possible special setup of clutch material and/or how tight they set things up. The key for a street driven C5 is to make sure the LSD does not chatter during a fairly tight figure 8 maneuver in an open parking lot. Also if you are road racing your C5 or happen to do a lot of track day events, then a different fluid maybe needed.
I think you are going to need more than 2 qts.. Especially since it's very difficult to get it all out...
I also squeeze several ounces thru when drain plug is out and empty just to "flush" out some crap in there.
You will need to add the LS additive IF you get any clicking/popping noises while cornering.. You'll prob be ok.. I Usually add it /