Sure Grip Oil

Although this is not the exact unit it's a strange trac loc clutch type differential
IN BIG LETTERS IT SAYS (DO NOT USE SYNTHETIC GEAR OIL) as does so many others, it's not for performance use.

Dana 60 Spicer Trac-Lok posi unit / 3 series / 35 spline

Dana 60 / S60 Strange S-Trac Helical Differential / 3 series / 35 spline