Try checking your guide rod mounts. You will notice them at the rear of your front wheel wells. I had a similar problem, most noticable when driving slowly up my unpaved driveway. Purchased and installed the Guide Rod Mount Kit and problem solved. Not the easiest DIY, but not terrible either

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1983 300SD -- 220k
1983 240D euro -- 225k - sold
2002 VW Passat W8 - Fast
1985 BMW 528e -- 356k - sold
1996 BMW 328Ic - crumpled into bits