Glen

Talking in general terms rather than specific to R class which I am not familiar with.

The pressure in the bag will be controlled by an electronic control unit and adjust pressure in response to inputs, principally the height sensor.

I would expect to see a height sensor on each side of the rear suspension, do a visual check first to make sure linkage is intact, not bent or been forced over center.

After that you will need it on a scan tool to check out live data & faults.

Cheers Aidan