Just read up and did fluid changes on 2013 Cayenne Diesel. Reporting that transfer case had issues, and that the 160k/16 years change interval for the fluids is NUTS, should be done way more often.
My 2012 Q7 TDI has the 8 spd auto (I think like the Cayenne). I would assume fluids have never been changed (close to 160k now).

Does my Q7 have same/similar issues as the Cayenne?

Should I change fluids NOW?

Are these fluid capacities correct?:

• Center Transfer Case: Non-locking Torsen Requires 0.50L of 75W-90 GL-4/GL-5
• Front Differential: Non-locking Open Requires ~0.50L to 0.80L of 75W-90
• Rear Differential: Standard Non-locking Requires ~0.80L to 1.2L of 75W-90

I used Motul Gear 300 for all 3 n the Cayenne. Same for Q7?

 

Yes, Change the fluids of all these, along with the transmission every 50k miles. If you find yourself towing much with the Q7, change them every 30k miles. Do a drain and fill and live happier along with your Q!

 

When trying to buy driveline lubricants for both our Q7s, a '10 (6spd Aisin) and '15 (8spd Aisin), I found they differed in both the transfer case fluid spec and the transmission fluid spec, but the differentials lubricant grade was same for both (GL4/GL5), which makes sense given it's the same platform, just diff transmissions, etc..

Point being to just be careful not to make assumptions, especially across platforms from Porsche to Audi, etc. In trying to build the ultimate luxury off-roader in combo with an excellent road car, it's likely that Porsche incorporated some mechanical lockers or antislip capability into their differentials on the early Cayennes, which Audi didn't give these Q7s (uses ABS system to limit wheel slip), so I'd be looking hard at those lubricant specs required for the Porsche diffs, etc. Example: On the '10 Q7 (6spd) it said to use the ATF fluid in the transfer case too. On the '15 (8spd), it said to use a VW specified Transfer Case Fluid only...think I bought the Liqui Moly or Ravenol branded transfer case fluid for ours, but same spec required.

There's also a component wear/fluid degradation/internal damage point beyond which it's not a good idea to change transmission fluid or differential fluids out, etc., like with those that have never been regularly serviced prior, or had the driveline lubricants serviced at all. If Porsche actually defined 160k miles (as opposed to kilometers, which would make a lot more sense), then that's pretty much worthless guidance, IMHO, as there's just not very much lubricant inside those units to start with...except for the transmission, of course.

If I were draining diffs/transfer case for the first time on a car w/160k miles on it, I'd clean off the diffs and xfer case first to avoid contamination, then capture the old fluid/lubricant coming out and examine it carefully for color/cloudiness/metal shavings/fragments, etc. There's chance that you'll end up with whining from the worn differential units if the old, nasty fluid was all that was holding them together still. Definitely keep/label the old fluid you take out just in case.

I looked up the parts manufacturers to research the correct service intervals to use.

Aisin's guidance on how to maintain either 6spd or the 8spd tranny working properly is by doing regular, defined interval fluid/filter changes at 50k miles, or if towing, then shorten the service interval to 35-40k miles, etc., and that's the transmission's manufacturer telling you how you should take care of it...they got no skin in the game otherwise. The rest of the driveline fluids/lubricants should be serviced at a minimum using the same severe service schedule, IMHO, again, as there's just not very much lubricant inside the differentials or transfer case housings, and beyond that they are just stupid easy to change out with the exception of the transmission, which requires a bit more effort and pre-planning, as well as a decent VAGCOM to get the fluid fill level correct on it. Also bear in mind that a pan drop w/filter change only nets about 8 liters, but the transmission system (lines, cooler, etc.) holds roughly 12 liters, so you never get all the old fluid out by doing a pan drop service, and thus why it's very important to do them as recommended by Aisin.