Q: Can I use regular power steering fluid in my Mercedes ML 350 or do I have to buy from a Mercedes dealer?
A: I won't be surprised if things have changed over the decades, but so far for the models of the 1980s and early-mid 1990s, I know that DOT-4 ATF (Automatic Transmission Fluid) was used for the power steering servo...as well as the autobox. I recommend you ask Benz dealerships or better yet, consult the owner's manual of the ML-350 in question. That's where you'll get the most accurate info.