PS fluid consensus
 

The BMW OEM power steering fluid is ATF, probably a German brand, like Pentosin, which is not readily available.
Reading through other forums, nobody really knows if regular synthetic ATF is OK, or if it needs to be Dexron III or Mercon V ATF.

If you would use any brand of synthetic ATF will the power steering seals deteriorate or not? If it's a "regular" Mobil synthetic ATF will it be OK? Or does it need to be Dexron III or Mercon V compatible?

RedLine ATF

+1. That's what I use on all of mine.

Vipers, Vettes, BMWs. They all get RedLine in the Powersteering systems and I've never had any leaks or failures.

Hopefully the link to this PDF will work for you...it was the last list I got that was up to date as of 11/2009 which lists the multiple brands recommended by BMW for power steering systems.

Your X5 would fall under "3.0" (which says to look at the table of brands under "5.0": http://bimmerboard.com/members/q/ori...0Type-List.pdf

Redline D4 is my choice too ( it's what I had leftover from the trans filter project )

:)

I used Mobil 1 ATF in my PS reservoir, no problems!

I've been using Mobil 1 ATF on my annual PS fluid change (turkey baster method) for nearly 7 years now without issues. No leaks or noises. I think I even use some Honda ATF a couple of times without issues.

Concur... Mobil 1 ATF... No Problems.

CHF 11s if your reservoir is so labelled. ATF otherwise. No mixing, they are not compatible.

If ATF, I would use any Dexron from any reputable major brand. Or Mercon. Not a synthetic, as what is already in there isn't a synthetic. There is no reason to hunt for a special ATF, in this case it is being used only as a hydraulic fluid and the ingredients added to different ATF fluids for different specs are essentially irrelevant in a power steering system.