O.k.,this can be caused by a valve block issue that distrbutes the fluid to the hydraulic shockes when needed to support the vehicle and ride and as well as to raise the vehicle.
The pump for this system is a tandem pump pumping both the power steering fluid and the hydraulic fluid for the abc suspension system,I dont think you have a pump problem here as in most cases the power steering would fail as well if it were.
You dont have any leaking shocks as there has been no leaks on the vehicle so what I think you have failing here is possibly a valve block that distributes the fluid and maintains the pressures and levels,this can bew common.
This vehicle most likely has two of these so the best way to find out which one or what is failing is to have the vehicle hooked up to the Mercedes dealers SDS machine to read out and repair any fault codes.Most likely they will find a valve block concern here that is at fault.
These can cost somewhere around $300 and can take up to 4 hours or more to install and bleed the abc suspension system.
Let me know if you need anything else,click accept if you feel satisfied with your answer as this is how I get credited for my time,Thanks Pete!