I've had an '88 300E since nearly new. It came with pirelli tires, not good. Replaced them with the proper sized michelins and it rode and handled much better and quieter too. 60K miles on it now. It's always been firm, A bit too firm to be honest for a luxury car. Suspension and wheels are stock.

I have a Porsche 928 of the same vintage and mileage that rides about the same and it's a sports/gt car.