A slow, slight drop in brake fluid level over a long period can be normal as brake pads wear, because the caliper pistons move out and more fluid stays in the brake calipers rather than in the reservoir. Large or rapid decreases in brake fluid level are not normal and usually indicate leaks or other brake faults that require immediate attention.
Stadium Auto Service in Ann Arbor, MI, specializes in brake service on Audi, BMW, Mercedes-Benz, MINI, Porsche, and Volkswagen autos.