I read a few years ago that modern ATF additives have gotten to a point where they will ruin seals in power steering systems. It happened to me on my 240D. Go to the parts store and pick up some power steering fluid. It's expensive, but it will save the seals in your system.
'01 C Class, Six Speed
'84 Euro 240D, manual, 533K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in