Don't forget to add the supplied friction modifier, which is used to reduce chattering. The recommended treatment is three ounces per quart of lubricant. The recommended additive is the commonly available type for use with GM or Ford axles. Do not add any more than needed, as it can decrease the oil's resistance to heat and oxidation and shorten its working life. As for the lubricant, Auburn recommends only a mineral-based SAE 80W90 gear oil, or SAE 85W140 if specified. Synthetics are not harmful to the unit, but can reduce the bias ratio due to their increased lubricity.