I have a 2000 ML55 and I can't get a straight answer on power steering fluid type and what is compatible. Is it Pentosin CH 11s, but that is a fully synthetic hydraulic fluid? Or can I use any type of power steering fluid? Does it have to be the Mercedes overpriced fluid or can I use ATF, can I use synthetic? Amsoil, Penzoil, Mobil 1? Thanks for your help.