Gear diffs

[HVAC25000]

Could someone give a bit of an explanation to the gear diff/oil thing?

First confusion lying in the fact that everyone is saying diff oil, but the setup sheet from, I think the japans, says diff grease. So, is it grease or oil? Oil is viscous liquid. Grease is semisolid. They're 2 very different things and the words are in no way synonyms... I'm assuming it's actually grease because I doubt those diffs are sealed up well enough to hold oil. Yes?

The setup sheet posted a bit ago said 20000 in the front (but the kit comes with 2000 I believe judging by the parts list, so is 20000 a typo?), and 7000-10000 in the rear. Another typo meaning 700-1000? Or is the parts list I received from Durango a type and it really is 20000?

What does a lower number mean, thicker or thinner?

Where can these different weights be purchased since Durango apparently only carries one weight.

Thanks!
Chris