Are there not drain and refill plugs?
I can't imagine there not being any! The procedure I used on my TD6 was this:
Buy 20L of Texamatic from a wholesaler's - it cost me around £80 delivered to my door.
Buy a vacuum pump type thing that fits the barrel.
Buy a new filter and sump gasket. These usually come with new bolts as well for some reason.
Go out for a drive and get your transmission fluid lovely and warm.
Make sure the filler plug undoes.
Undo the drain plug - obviously with a suitable bund underneath and whilst wearing latex gloves et al.
When there's very little fluid coming out, refit the drain plug.
Top up the fluid until it starts coming back out the fill plug.
Leave the fill plug out, start the engine and run the gears up and down a few times, pausing for about five seconds in each position.
Leave it in neutral with the engine still running and fill up further. Depending on your pump you'll get a few more pumps in.
Refit filler plug when it starts running back out.
Get a good few miles on this lot of fluid, then repeat those steps above, starting with number 4, obviously.
Each drain and fill done like that takes around five litres, so I did that twice then did a final drain which included dropping the sump and changing the filter. I gave the sump and magnet a right good dose of cleaning as well. The last fill took more like seven litres. In retrospect, I'd have bought another five litres of any old ATF for the first drain and fill, provided it was Dextron III - it would only really be getting used as a cleaning fluid for fifty to a hundred miles.
I have done two drains as you have explained above, but this will still have contamination, there is a method I have heard of when I had my first skyline which was to remove the oil cooler pipe and pump out the fluid at the same time as pouring in new fluid until it runs clean, this method flushes out the tc and valvebody etc
Not sure how to perform that on the RR though
How much would a job like this cost if you did it yourself?
I got mine done at the local Land Rover independent specialist.
$350 for the driveline service which included the cost of the fluids + the labour.
They flushed the transmission fluid (changed the filter too i believe), the transfer case, front + rear differential fluids as well.