I purchased four genuine MB 18mm 3 burl spring pads. To my eyes, the car does not appear to sag. That said how can I know for sure? If it is sagging I want to go ahead and purchase new springs so that it is factory original.

Probably the factory service manual gives points to measure to from the ground. Actually years ago Mercedes maintenance gave the interval to change springs at. Measuring for the need makes more sense to me.

If it looks fine I'd leave them alone until one breaks, which is unusual.

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.