I'll be taking mine apart in the near future, they are usually not very difficult. Between the exploded diagram and what you see/learn taking it apart it becomes much easier to put back.
30wt oil will leak out over time, but it will provide lubrication. In the past I used to pack with grease to lock the diff up more but the grease packs and slings too much and after a few runs its not very stiff anymore.
I think it's better to use thick diff oil instead of grease, it provides more consistency. I bought 100K, 500K, and 1M cSt diff oil online (team associated) for about $9 each, to use in my Typhon. Im planning to rebuild the Fury diff and use 500K in it.