Mercedes makes a "nerf" cylinder to be retrofitted into the coil springs in the seat frame. I don't have the part #, but may have it at home. I'll look tonight. I have put them in my seat and they help. They are multi colored compressed foam in a "camoflage" pattern (kinda blackish, brownish and greenish/tan). If yours are all one color, in a "neon" hue, then someone used a section of pool "noodle" in there, which, I understand, works well.

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The Golden Rule

1984 300SD (bought new, sold it in 1988, bought it back 13 yrs. later)