MB springs rarely sag. I believe most ride height problems are caused by suspension components other than springs. But, smetimes the bottom coil will break after years of hard winters (rust). I would suspect possibly the wrong struts/shocks were installed, or front end suspension work (e.g. lower control arms) was done incorrectly, or springs were 'tweaked' at some point. How low is the front/rear? Dealers use angle gauges to detect ride height problems. Try measuring from the center of the star on the wheel to the underside of the fender lip.

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Brian Toscano