The most important thing is that it is a silicone grease (all 'diff greases' are).
If you use an oil-based grease such as those used for ball bearing assemblies, you will get uncontrolled slip in the diff quickly leading to burn-out. This is because oil based greases get thinner under shear loads, like between the balls and rings, effectively increasing their penetration and lubricating effect. So they end up lubricating right where you don't want it - between the balls and rings.
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