Try checking out your sway bar links. When they go bad they usually manifest themselves as a clunking going over bumps. This happened on my 123 wagon. It's easy to check them. They are part of the rear suspension. An S shaped link I belive yours are metal. There have a pivot point on either end. If you unbolt one and pull it out, then you can move the pivot points by hand if they are wobbley or easily moved they are bad. If they are stiff then they are good.

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