gear oil, reuse or not
If it's clean I don't see why not reuse it, typically gear oil is good to around 30 thousand, IMO.
It is a maintenance item, some will disagree, but I change mine in my truck, both front and rear 25 to 30 thousand.
If you're dropping in a suregrip, don't forget the friction modifier!
Also, if you have a small magnet that you can stick in the bottom of the case, that is a plus, it's not a necessity, but it can catch any shavings that come from normal R&P wear.. Just keep it to the side that the ring gear isn't on.