Dex410v4 diff oil

[martinw76]

Whats the best make of diff oil I should use

[mattr]

Any of the big brands will be fine, losi, ae, ultimate and so on. Only thing to think about is the ratings of the oils. Do you want cst (repeatable, consistent, internationally controlled spec.) or weight/wt (made up by manufacturers, different weights depending on batch/supplier, pretty much uncontrolled).
If you go cst you can buy oil from anyone and it will be what it says on the packet.
If you go weight, you pretty much have to stick with the same brand indefinitely.

And for a 410 I'd probably buy 3, 5, 7 10 and maybe a12000 cst to experiment with. Unless you already have a good recommendation for your local track.