Power Assist Brake Vacuum problems of the 2007 BMW 525

The contact owns a 2007 525 BMW. The contact stated that without warning, the brake pedal would become stiff. The vehicle was taken to an independent mechanic where the technician diagnosed that the vacuum booster had malfunctioned due to contamination. No repairs were made to the vehicle and the manufacturer was made aware of the failure. The failure and current mileage was 120,000.