The Pentosin was developed to reduce steering noise when COLD.
Mechanically, it is the same PS pump, same vanes, just different recommendation b/c of noise complaint.

Mine has Pentosin and still whines a bit when temp is < -10C, so go figure!

Personally I don't think it matters that much, in a pinch use Dexron-III and chances you will be fine. Don't sweat over this BMW thingy.