I replaced the rear springs on my 300D a few years ago and adjusted the rear end height using spring pads with different thicknesses. You should replace the rubber shims/spring pads if they are damaged. As Mattman wrote, the pads are used to correct the height of the rear end using pads of different thicknesses (as well as cushion for the spring to body contact area). When replacing the springs take a note of the part number on the spring pads (if it can still be seen) and measure the thickness of the rubber on the top portion of the pad in a place where the spring did not make contact. The adjustment is done after you replace the springs using the old spring pads with shocks installed and put the full weight of the car back on the ground (a drive around the block will help to let the suspension settle into its working position). Then, on a flat surface, look at the rear of the car to see if it is level or not with an empty trunk and, as I recall from the M-B manual, a half full or so tank of fuel. If the rear end is level looking at it from the trunk end facing forward, then no adjustment is needed. If the rear end is not level, then you need to buy and install pads that will level the rear end. This may take replacing one or both pads to achieve a level rear end. On a flat surface measure the difference in height from one side of the rear end to the other to help determine the pad(s) that you need.
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1977 300D: 300,000+ miles
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