I know KW used to sell coilover suspension packages for the W124. It doesn't look like they offer them anymore though... http://www.kw-suspension.com/en/30_Products/60_Product_Finder/index.php?modell_1=E-Class&level=3&hersteller_1=MERCEDES&gruppe=all

My 300E is stiff and flat with Eibach springs and swaybars with Koni adjustable shocks however, it still doesn't feel as balanced as my 500E. When was the last time you changed all your suspension rubber? They wear over time and add a lot more slop than you'd think they would.

If I remember correctly, The AMG hammer had a 25K PM cycle on their suspension bushings and sub-frame mounts.
I'd imagine 5K on the flex disks!

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Current Stable:
01 ML55 AMG
92 500E (a few mods)
87 300E (lots of mods)
00 Chevy 3500HD Diesel Box Truck
68 18' Donzi Marine
06 GT i-Drive7 1.0 Mountain Bike (with GPS!)

PREVIOUSLY OWNED:83 300SD, 87 420SEL, 88 420SEL, 90 420SEL, 86 560SEL, 86 190E 2.3-16V AMG, 94 E320