No recommendation but for myself the Fluid sort of gets changed when I work on the Calipers and I bleed the Fluid out until clear.
Other than that as long as the Brakes work I am not concerned about the Fluid.

They sell the Denatured Alcohol to clean the system out but I have never seen or met anyone who as flushed the system with that before adding new Brake fluid.

I also do not see any difference between the Mercedes Brake System and other Brake Systems that looks like it needs any special attention or procedures.

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84 300D, 82 Volvo 244Gl Diesel