I don't know what the fluid change interval (if any at all) for the Hydraulic self-leveling suspension.
The fluid change interval required by Mercedes Benz for the Brake Fluid and Radiator coolant is as follows:
1. every two years for the brake fluid.
2. every three years for the radiator coolant.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".