I have a 1992 400E with 165K miles and it does have the serpentine belt.
I have read a lot of posts and debate on Power Steering Fluid type and am still confused. My Owner's Manual say MB Power Steering Fluid (nothing about ATF, Dexron II or anything).

What is MB Power Steering Fluid in terms of composition and what is in it?

Auto Parts store yesterday told me they thought Pentosin CHF 11S was right, which is a Mineral Oil based fluid at $30/Quart!! They could not find a definite equivalent reference so I do not have high confidence.

Is there a filter on this Power Steering system?

Thanks,
Kim

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1992 400E (W124) - 177K Miles - fun car!!