I just sold an SL to a buyer that noticed the car was not as solid as her 1980-something 300SD, and I was reminded of this old thread. My experiences with owning several 129s over the three years since confirm for me what I wrote then. This chassis is particularly sensitive to imperfections in wheels, tires, and road surfaces. With the top down, any of these will produce a considerable amount of cowl shake which is greatly lessened with the hard top on the car.