Went through the process of changing the automatic gearbox fluid in the patrol recently and it was a cool but also expensive learning experience to say the least.
I had noticed a while back when I changed the main radiator that the gearbox fluid was bad. It was black and the viscosity was more like water than oil, clearly it was very old and may even have been the cause of the sporadic and random limp mode events in the past.
In the Haynes manual it states that the fluid capacity for the 5 speed auto in the 4.8 is 11L so I bought 12L of Nissan Matic J to be safe. The instructions are that one should drive the vehicle until the fluid is at normal operating temperature and then remove the transmission sump plug and drain the oil from the sump. Then replace the sump plug and refill with the same amount of fluid that came out, checking the level on the dipstick to be sure. I did this and only got 5 of the supposed 11L out of the sump.
The torque converter is still full of bad oil, how to get it out? I was then told that I can take off the hose that brings the fluid to the radiator for cooling and then start the vehicle. Let the vehicle idle and the fluid will pour out of the hose. At the same time I should pour the new fluid into the filler tube. Continue with the process until the fluid coming out of the hose becomes pink and new and not old and dirty. That way you know you got 90% of all the bad fluid out.
So that's what I did and low and behold my 12L of new fluid was not enough to flush out all the bad fluid, so then I bought another 5L and that did the trick. The fluid coming out of the hose became relatively pink but not completely. I reconnected the hose and then following the instructions in the Haynes manual I started the vehicle and let it idle for 5min until the engine was warm. Then you slowly cycle through all the gear selections and then put it in park and check the level while the engine is running. The dipstick was basically dry, just on the lower end of the cold range on the dipstick
this means another week of waiting and another 5L of new fluid. This is a pain as I have to get the fluid couriered from Gaborone all the way to the tuli block which adds to the already expensive fluid and takes time, plus I think the guy in parts must think I'm drinking the stuff by now 
Obviously as you pour the new fluid in it mixes with some of the bad fluid and so you end up using more doing the flush in this way. Anyway the point is that draining the transmission sump of its 5-6L of fluid and then topping up with the same amount DOES NOT constitute a proper fluid change in these gearboxes as the torque converter still has 7 or 8L of bad fluid in it that will mix with your new sump fluid as soon as you run the vehicle and render it pointless. So check this with your dealer or mechanic the next time you get yours changed. What is the change interval? Well the manuals say between 45000 and 75000km but I would change it as soon as it starts to change color from pink to black. If you tow or spend alotnof time doing strenuous driving the interval will be shorter.
By the time I get the balance of the new fluid and correct the levels in the gearbox I will have used about 22L of nissan matic J at a total cost of P5630 or R8170. At least I did it myself so there was no labor charge.
Hope this is useful to someone
Cheers chaps
