Just wanted to share my experience on changing the transfer case fluid.
My buddy's Cayenne only had 25k on it but I strongly suggested doing it.
Super easy. Didn't even have to jack the car up which is probably better since the car is nice and level.
Screwed off the top plug first then proceeded to unscrew the bottom plug to drain the fluid. Yup, pretty dirty. But not burnt or black.
I used the Ravenol transfer case fluid which has a built in spout that fits the transfer case opening perfectly. (I'm kinda liking the Ravenol products!)
One thing to mention, the transfer case capacity is a bit under a liter. There are numerous posts that mention needing two bottles of fluid but you only need one.
Used some sealant on the threads and LIGHTLY screwed the plugs in. Just a bit past hand tight. But no more.
Hopefully good for another 20k.