Hi there! I have a 2000 S430 with exactly the same problem. Last year, when temp gets to around 0 degree F, both rears would sit on the ground. When temp goes back to around 5 degree F, the problem would be gone. This year, when temp is around 8 degree F, both rear sinks.

I just replaced the suspension valve by the right front wheelwell. That did not fix the problem.

So I ordered 2 rebuilt rear struts today.

If anyone can help... between the suspension valve and each of the rear strut... is there only a continuous line between them? Or is there fittings that can leak?

Anyhow, I am so tired of this problem... every winter my Mercedes would not be driveable for a couple of weeks because of this problem...

Hopefully the rebuilt struts will solve the problem. I will get the struts next wed and I will let you know if that solves the problem. You might just need 2 rebuilt rear struts!

Wish me luck!