I'm having the exact same problem with my 92 300se. For the longest time the steering was nice and firm, basically a perfect feel. Then, randomly and about once a day, I would hop in and start up and my steering, until I turned the car off, was extremely easy and sensitive. It was a full 180 flip from what I was used to.

I started think maybe the easy way was what my car was supposed to be like and the previous way, being somewhat firm, was wrong.

Yesterday my steering became extremely hard to turn. It feels like the power steering pump is not even operating. And it basically has stayed like this for 2 days straight. It's a tricky problem.

Today I ordered a new power steering pump filter and I'm gonna replace the fluid and the filter early next week. I'll post up the results so that anyone else that may have this problem can have some insight for a solution. I will use DOT4 I believe.

If you, oteixeira, are still having this problem, clue me in on any steps you've taken to fix this. If you're steering is as hard as mine is, hopefully you consider something soon. My mother would not be able to even drive my car the steering is so hard to turn.

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1974 240d "Peace, Love and Empathy" - Kurt Cobain
1982 300sd "It all depends upon the Benz!" - Me
1983 300sd
1985 500sel
1992 300se