Mercedes-Benz with Active Body Control or ABC have a number of factors to be concerned with. This system is a completely active hydraulic system driven by a high pressure pump that also controls power steering.
These systems are prone to leaks and seeps but are overall very reliable with leaks at the pump being uncommon. The vehicle level is controlled using inputs from four level sensors and accelerometers.
By routing high pressure fluid, delivered through valve blocks, the system also has nitrogen accumulators for dampening. The valve blocks have valves with metal seats and these can be prone to leaking if the fluid has fine particles of dirt in it. It may be necessary to flush the system in the event that valves are suspected of leaking or the ride height changes after shutdown.
This uses several gallons of Pentosin CHF 11S hydraulic fluid. These systems are complex and diagnosis and testing should be conducted before commencing any repairs.
The ABC struts have quick release connectors, given where they are located corrosion often prevents removal requiring the corresponding hard lines to be replaced. Never work on these systems when they are pressurized. In many cases they are self bleeding but several test modes are available for these systems that can be used for diagnostic purposes as well as insuring bleeding is complete.