I see this thread is old (but so am I) - my clunk is seasonal. During the week or so of cold weather (below about 50°) here in Florida, my 300SD clunks so hard on slowing and downshifting to 1st, that I have to check the rearview mirror to make sure I haven't been rearended. I see the roots of this thread point to either flexdisk (rear suspension issues) or vacuum regulator. Which of these might best fit the scenario of clunking only when the ambient temp (not the engine temp) is cold? Thanks