Genuine Mazda 6 Brake Master Cylinder Cap. Is your Mazda 6 brake cap missing or leaking? Replace it with a new Mazda 6 Brake Cap. Genuine Mazda 6 Accessories and Mazda 6 Parts offer the style, comfort, quality and satisfaction that make driving a Mazda 6 even more rewarding. Designed and guaranteed to fit your Mazda 6 perfectly inside and out, they are the only accessories built to the same quality standards as your Mazda 6.