In a healthy brake hydraulic system, you should not “lose” fluid; it is a closed system. The only normal decrease in brake fluid level you will see in the master cylinder reservoir is from fluid moving into the calipers as the brake pads wear, but the total system volume remains the same. This drop in brake fluid level will occur very slowly over a year or more. If the brake fluid reservoir level is dropping faster than that, there is usually a brake fluid leak or a component, such as the master cylinder or power brake booster, that is allowing fluid to escape or be drawn into the engine.
Power brake boosters on newer German autos are powered by engine vacuum. If the seal in the brake booster becomes worn and leaks, it will suck brake fluid from the master cylinder and decrease the brake fluid level.
The brake technicians at Stadium Auto Service are German auto brake specialists. If you have any brake problems on your Audi, BMW, Mercedes-Benz, MINI, Porsche, or Volkswagen, please get in touch with us for a brake inspection or brake system diagnosis.