http://www.hotrodheaven.com/comments/messages/1888.html
If anyone can help with questions regarding posi lube, what is it good for, and what is the best one, have a ball. The above address will take you to another place I posted the same question and the moderator was interested in hearing from others also. Thanks for your input!

It's good for traction compound, Josh. Pour it on your tires to finally get under that 12 second wall. Put water in your diff, that'll keep down those 700 degree temps!
Bryan http://www.chevelles.com/forum/wink.gif

OK Josh, As far as I know, posi lube is a special formulation of some kind that somehow manages to lube the gears and bearings without affecting the action of the clutch pack. You NEED to run it in a posi type diff. It won't hurt an open rear, but it won't make it any better either. Couldn't tell you which brand is best, all my lubes are Valvoline products. If you're looking for speed, go for the lightest weight you can find. Hope this helps, Bryan

I always use the $6 GM limited slip additive. Put one small 4oz. bottle in then fill up the rear with standard 80w-90 gear oil. This will keep your posi from making clunking noise and operate properly. The additive is a friction modifier that allows the clutches to slip around corners but still hook up in a straight line.

I agree with Bob 100%.

I used to have "el chiepo" posi oil in my old axle and it began to slip under heavy use, specially in the corners when turning right. Then I got another posi and bought GM oils AND THAT SMALL ADDITIVE BOTTLE. No problems ever since. It does two wide black stripes whenever needed....