W210 has developed a sag.....
 

in the port quarter. 2000 4matic wagon, 179K on the clock and when she sits idle for more than 2 days, a left rear sag about 2"-2.5" happens.
The hydrolic resevoir is full, right side is OK and ride is good.
Is this a checkvalve or seal that allows the fluid or pressure to vent to atmosphere?
What are the most common causes of this issue? Thanks

I have searched for tips here, can ANYONE help with this?
What to type in the search box?
What to check for under the car?
Anything?

Are you sure you don't have air springs on this unit? Sounds like you have an air spring leaking down.

Its a hydraulic rear suspension with a level control valve actuated off of the rear sway bar. Id expect the valve failing in the absence of an external leak. Logicly any other failures in the system would cause both sides to sag.

If it were me I wouldnt worry about it as long as it pumps right up when running.

Thanks Duxthe 1