Diffs are easy to oil change, all you need is a half inch ratchet.
On the diff casing you will see two half inch square plugs, one on the bottom and one in the middle of the pan lookin straight at you. remove the one lookin at you, then with an oil catchin pan under the diff remove the bottom one and let the oil drain out, replace bottom plug then fill diff back up to level with fresh EP90 OIL.
Transfer box is straight forward too, again there is a half inch plug on the lowest point of the casing which you remove to drain, the filler plug is either a plug like the others or a square post on the back of the box near the handbrake drum, this is also filled to level with EP90.
Not sure about the r380 gearbox drain and fill plugs as i have only ever had lt77 boxes but im sure someone will advise :scratching_chin:
When doin a service i will take the landy for a run to get it up to operatin temp then park it up and drain all the oils while they are nice and warm and runny as cold EP90 is hellish slow to drain