If you notice that the brake fluid level in the brake fluid reservoir has fallen to the MIN mark or less, check the brake system immediately for leaks. Also check the thickness of the brake linings. Contact a qualified specialist workshop, e.g. an authorized Mercedes-Benz Center immediately.
Do not add brake fluid. This does not correct the error.

Only check the brake fluid level when the vehicle is stationary and on a level surface.

The brake fluid level is correct if it is between MIN marking 2 and MAX marking 1 on the brake fluid reservoir.