Oil is a item many owners or garages seem to ignore, why this trend is increasing I'm not sure but its not a sign, every Range Rover I have carried out oil changes on has been very disappointing.
Firstly transfer box oils are not being changed and if they are changed the wrong type of oil is being used, I've drained out SAE90 oils on many a transfer box and with very high metal content, not only is the wrong oil damaging but its effectiveness to be cooled is not going to happen.The correct oil for the transfer box is ATF (Automatic transmission fluid) Dexron III, other brands list it under other types for example Shell call it Donax.TA, TZ etc
ATF is used in the transfer and auto box along with the power steering but check with supplier if it can be used in all as some are listed not for power steering use.
I Prefer to use Shell Helix Diesel 15W40 or Shell Helix 10W40 HX7 as they offer great protection on the Rover V8 motors with its flat faced hydraulic lifters.
Another good oil is the Castrol Magnatec, along with the Shell Helix HX7 they are both Part synthetic oils.
It is not wise to use a fully synthetic oil on a medium to high mileage Range Rover II
Ever walked into a spares shop and noticed the odd cheaper oils on offer vs the known brands like Shell, BP, Castrol, Mobil, Caltex etc, compare the prices and you'll notice a substantial difference, now ask yourself why....... Many cheaper oils out on the market are simply junk and can and do contribute to carboned up piston rings and valves carboning up, Its one of many reasons why I insist on a good branded oil in any engine.
I have walked into many garages (including dealers) and have seen the cheapo oils laying around.
Its all about profit and the ignorance of understanding quality oil's vs the cheap junk.
The pic below is from one of the many Range Rovers axle oils that has been drained.