The most likely reason is that you need new accumulators. These are the spherical things mounted near the rear axle.

They are not too hard to replace, and cost around $100 each.

Do a search on accumulators. Lots of info in here.

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Semibodacious Transmogrifications a Specialty

1990 300D 2.5 Turbo sedan 171K (Rudolf)
1985 300D Turbo TD Wagon 219K (Remuda)

"Time flies like and arrow, yet fruit flies like a banana"
---Marx (Groucho)