"With the weight of the car resting on a jackstand under the control arm, not much short of the epicenter of a big earthquake is going to knock it off. If the jack supporting the control arm looses pressure or slides out you're going to be in deep yogurt. Jackstands don't have wheels!!! Jacks should only be used to lift a car. For any underneath work jackstands must be used, and I would NEVER,EVER rely on a jack to keep a spring compressed while I'm there doing any work."

Duke, since you live in SoCal (as do I), we know that the "...short of..." happens a lot more than we like. This worries me when the car is up, and it is precisely because the jack has wheels that I rely on it as safety backup if a tremor hits. I use jack stand as primary support - the jack itself, wood blocks, free tires and wheels, whatever, as my safety backup.

Jackstands are only good if NOTHING shifts. If the car is intrinsically unstable on a jackstand, you may not know it until everything shifts suddenly due to a force vector that is not in-line with the jackstand axis of support. A mobile jack will tend to move withthe vehicle, or direct the vehicle motion in the free-motion direction of the jack, keeping it up.

I have never replaced struts on the Benz yet, and would judge about using compressors for stabilizing the springs before doing so. It seems like good insurance, though, and they are cheap to rent.

Steve