Hydraulic Suspension
If this is fine than it might be worth taking a trip to the dealer to make sure their is nothing wrong with the Airmatic system on the W211.
You dealer should be able to attach a DAS computer and see if the suspension is throwing any faults. I believe they look at the voltage level coming from each of the sensors.
I had a total airmatic failure earlier this year where the airbags would just dump all the air out when I parked my car. Your symptoms don't see that this is the case, but i would get it checked.
BTW, you didn't unload any cargo or passengers before examining the height I presume?



