One thing to know is that you need oil in the diff and grease in the hubs. The seal between the two goes and you end up with oil in the swivels. Don't worry. All this can be sorted with the axle refirb. But, what you do not want is grease in the axle. This can have pretty catastrophic effects on the diff. If you are going to look at an 80 in detail, you should be taking a 24mm socket to remove the filler plug on the front diff so that you can see what's in there. It's not easy, but if clear oil runs out then it's good news. If there's no oil as it's run out of the swivels, well, again it's something to think about. But if there is soup in the diff then it's really not good news. However, this worst situation is generally the most rare.
No I'm not bidding. I want something a bit tidier than that