Pentosin CHF 11S is what your after there, ATF is also fine.
I have had excellent results with Shell Donax TX, incidently this Donax TX can also be used on the 540's transmission (5HP30) with stunning results, and the stuff is dirt cheap. If your considering buying, buy a 20 litre and flush your gearbox as well, here its about R50 for a litre, so thats really not a lot of money.
Also, here is a scary fact, your power steering fluid is actually shared with the booster side of your braking system, called the H31 braking system.
If you are loosing fluid, it may be at the brake booster, its a very common place to leak from.
If your standing in front of your engine, on the back in the right hand side, you will see the master cylinder attached to another long cylinder, thats your brake master. Where the brake master and brake booster meets, (a little triangle), right there is where it leaks from, time and time again.
Give me a pm if you need any more information on this one.....
My Rides :
10 F10 535 (mine)
12 F30 320i (wifey)