Brake Pedal And Linkage problems of the 2011 Mercedes Benz C300

Brake pedal is notchy or sticks during the initial portion of pedal travel. Inconsistent brake feel at each stop leads to over or under braking, depending on whether or not the pedal sticks. It has been diagnosed by mercedes as an internally leaking brake booster, but they won't replace it, saying the part falls within specs. This car is a 2011 C300w4. This model is not listed in your pull down menu (I entered e class to complete the form).