I prefer either Corally Ball Diff lube, or Kyosho 30000 Diff Grease. The quickest Mini at my local club uses 300000 Silicon Diff Oil, but it does leak a tiny bit from the outdrives.

Tried various industrial and commercial grease's, none do the same job as the above.

One racer swears on water pump lube from days gone by, but we cant find anyone who sells it now.

Railway grease would work