[Hoborg]

All this producer talk is marketning like somebody says. Oil is anticipaded for all transfer box life but no one , even BMW, not say for how long is calculated life of transfer box. It generally depends on how the car is used. But the truth is that the oil is contaminated with debris from wear on the clutches and loses its properties due to moisture entering the gearbox through the breather. The technical condition of the clutches in the gearbox is also the main factor determining the oil change. If the clutches are operational and the oil has been changed systematically from the beginning of the gearbox's life, you can change the oil without any problems, but if it has driven more than 200,000 km and the oil has never been changed, there is a high risk that after changing the oil, the gearbox will not drive for too long. Especially when the car didn't have an easy life ...

[XuLeTZ]

So this is me with my F31 320d 2012 on 215k miles.
Oil every 7k miles or 12 months (Coded the car to ask for oil every 7k/12m rather than 18k miles/24m)
Gearbox every 60k miles or 8 years
Differential every 2 years, in the same time with brake fluid. (this is not required that often, I think 3 years is safe anyways)
Not a single issue with the engine or gearbox.
Owning the car since 2018 and had 110k miles 4 years later 100k miles

[bmchicago]

my recommended service intervals for non-M
transmission oil service = after transmission is repaired.
transfer case = when transfer box is repaired, or when the FC is stored
differentials = when differential is repaired

if you get 100k miles on these units without service that is great.
changing the fluid is wasteful and usually does not extend the life.

E53 m54, now 200000miles and differential and tranafer case never replaced never serviced. Only oil changes. So do not agree.

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It sounds like you made up your mind, go ahead and change it. Nothing wrong doing something you are determined to do, as long as it doesn't cost you excessively.

Not my car, I am collecting other people's experience for customer's cars.

i think you are confused, because based on your own experience, you agree with me

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Changing the fluids won't do any harm at the end of the day. Not changing them may not do any harm either as many of you have experienced. It's all just a matter of personal preference I guess.

changing the fluids MAY damage the transmission. 
when the transmission ages, the fluid becomes thicker due to the wear in friction material. the transmission will calculate fill times to attempt to adapt to wear.

if after transmission fluid exchange, fluid is now thinner due to loss of friction material and can damage the transmission due to sudden pressure changes.

[XuLeTZ]

What if you are resetting adaptations after gearbox fluid change? I`m talking about ZF8HP.
I have done 3 so far and 4th fluid change is coming in 30k miles (1 year tops).
Everytime I done it by the book, oil warmed up etc. and then ISTA and reset gearbox adaptation. First 300-500 miles is a bit rough but after that is learning my driving style and smooth as anything. again, mine is on 210k miles and gearbox is still smooth. Maybe it matters that 90% of the time I`m on motorway, for the city I`m using wife's car (petrol)

[willisodhiambo]

The fact that there are transmission failures with new fluid, unchanged old fluid, and even a few thousand km after production proves more that it isn't so much related to the fluid, but rather something else.
I think many do it because it's something you can actually feel you have control over, or because a shop said to do it... Or the ZF website said so.

That being said, I changed the fluids, but without the thought that this would actually guarantee a longer life. There probably is some benefit to fresh fluids. I don't think there will be solid proof, or else these debates wouldn't exist.

While there, change aged mechatronics seals for the best results.

This is very true!! I have seen failures at less than 100K and I have also seen good boxes way older than 200k without fluid change. And the fluid in these old boxes was not terrible.

I have also seen a box go bad after service, for no clear reason. It is a gamble. Clutches will wear out. New fluid will not help that. But like all things if anyone gets comfort from servicing a gearbox at every 10K, why not!! No harm at all. Boxes and engines are different. The oil in the engine suffers hellish conditions. Gearbox oil has it very easy in normal use.

Not in my life have I serviced a differential

[m1ke]

I do at 50k miles for diff and transmission. Or when I buy it if the car is over that mileage. If very high miles I wouldn’t touch transmission oil in a zf auto though.

[Netocassion]

Driving a 530e (2nd owner). Mileage is 120.000km. Did a oil change in a transmission. There were no oil changes so far before that, that's for sure.
To my surprise Original oil in a transmission was still transparent (not fully but rather a noticeable transparency). Don't really know how this happened but this is a true story.
In a meanwhile a good friend of mine has a 520d with ~70.000km and his transmission oil was black as a crude oil. Color is not showing the state of things, I know, but still..

Considering the faulty behaviour after an oil change, my PHEV has a rare tendency to have some kind of a "confused state" when it needs to shift a gear and to start a petrol engine at the same very moment. It seems it fails to make up a sequence what to do first and that's why the engine is rumbling for several seconds and the gear is not shiftted for those seconds as well. It feels like it is synchronising the harwdware or something at that moment, but again - extremly rare situation.

[bmwlover]

I do at 50k miles for diff and transmission. Or when I buy it if the car is over that mileage. If very high miles I wouldn’t touch transmission oil in a zf auto though.

Why will not touch?