I might have the same problem with my 1997 E420. I just got it with 130K miles on it, oversized tires 255/45/18".
When I hit road marker (yellow reflective road markers or ceramic bott's dots) while cruising 40 mph or more the car tends to sway left and right and needs corrective streering actions.
Is it oversized tires problem or shocks or what else?
Appreciate any inputs and advices

frank