My car only manifests these symptoms during very strong cross winds at high speeds. Most cars will suffer in these circumstances. I agree with the comments that the C is not an S and cannot be expected to bear the same refinement.
I drove the car at 100 mph last night and took my hands off the wheel. Wind was moderate. I could feel the wind on the car. However, the car tracked very true and very straight with no hands. It occurs to me that this is another example of the chassis's communicativeness being mistaken for weakness.
As a driver I want the car to talk to me about the conditions outside: I should not mistake those messages for flaws in the set up. This is particularly true in corners. At first I thought the car had very low reserves of grip; then I realised that what I thought was the feeling of the car losing control was simply the feeling of the chassis dynamics. I now find the car very satisfying to drive in bends; there is a great deal of warning before the car starts to lose grip. Grip is lost progressively rather than suddenly.
NB: John/BlackMercedes: my tyres are not warranted under the signature programme; rather MB dealers cannot sell the car as a Signature car unless there is 4mm of tread on all 5 tyres and at least 3,000 miles to any service. My car's tyres were worn and it needed a service when it's previous owner traded it in, so the dealer fitted new tyres and gave it a B service.
I would really like the 17 inch AMG wheels from the C43; I am concerned at what body work mods will be required. I still cannot quite understand what is meant by fender rolling: is there any visible difference to the wheel arches? Should one fit AMG springs and shocks with those wheels? How would such a suspension set up interact with the seat springs?
Of course all elements of the car's suspension are tuned to match: tyres, wheels, springs and shocks, seats.
1999 SL 500
1993 320 TE
1986 500 SEC