Rear air suspension S211 (not airmatic)

[Gollom]

Bit at my wits end with this one! My 2009 S211 drops on rear near side when parked overnight, but here's the thing - only does it three times out of seven! Other times it does not budge

Lifts well when I start the car. Visual inspection of the bags etc. does not show any issues and the air lines have been replaced.

Any thoughts on what else we could look at? The obvious thing is to change the bags, but given the issue manifests itself sporadically I don't want to replace expensive parts (and of course I'd replace both) then discover I still have a problem.

Any help appreciated (I've seen other posts, but they do not seem to have this occasional issue)

 

[merc85]

Could be alloy corrosion where the rubber hose from the bag fits onto the alloy tank. The alloy gets porous over time Alps had a similar issue i believe.

 

[steveq]

It is worth checking the level sensors. They can rust and break. The intermittent nature of your issue makes diagnosis difficult though.

The likelihood though is the air suspension units are failing. They are 11 years old so are probably perished.
On my S212, I found that the temperature effected the rate of dropping but basically they were worn out -- and that was on a 6 year car with just over 90K miles.