I seem to have a similar problem on my 123. A lot of times when I come to a stop the car makes a thump/thud. I have not checked any or the parts sugested, yet. I also have a small shimmy at 55mph+, the steering just vibrates left and right, but I think this is because I need an alignment. The thunk seems to be coming from the front left area of the car. I want to say that it is coming from the (forgime the lack of technical language) the connector that ties the wheel to the chasis, the one that goes back and inwards from the lower arm and into the chasis. Is it possible there is some play and it makes the thump?