That FSB is vague and misleading.

What are "special additives"? STP, PowerPunch, Slick 50, Lucas additive, Marvel mystery oil...?

What is the "recommended lubricant" that can only be used? Sounds like it is NOT standard gear oil.

The following quote is taken directly from Auburn's website under cone type limited slip differential- Installation Manual:

-IMPORTANT LUBRICANT NOTE

The Auburn Gear limited-slip differential design has been extensively tested with high quality non-synthetic 80W90 hypoid oils treated with GM or Ford friction additives (3 oz. of additive will treat 1 quart of oil). To avoid differential clutch chatter (noise) and for optimum
performance, use the oil and additive described above. Use of other additive and oil types may cause differential clutch chatter.**

Ford Part Number: C8A219B546A
GM Part Number: 1052358

**Note the similar terminology about "other additive and oil types" that should not be used.