When the springs were replaced, were the correct ones installed? There are different springs for different configurations of rear suspension on these cars.

There are also different thicknesses of spring pad used. Were they replaced with the springs? Correct thickness used?

I recently redid the rear springs on my SDL due to the "squatting dog syndrome" and used Lesjofors springs. They raised the rear end up roughly 1" and made a profound difference in how the rear end rides with passengers or junk in the trunk.

Other things that can affect ride height in the rear: subframe mounts and differential mount.

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Current stable:
1995 E320 157K (Nancy)
1983 500SL 125K (SLoL)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Gone and wanting to forget:
1985 524TD 167K (TotalDumpster™) [Definitely NOT a Benz]