Genuine OEM Audi Brake Master Cylinder Reservoir, part number 4K0698301. This component is designed to store brake fluid, supplying it to the master cylinder for the hydraulic braking system. It is positioned directly on top of the brake master cylinder. Weighing approximately 0.289 kg, this reservoir ensures a consistent supply of fluid to maintain braking performance. Choosing a genuine OEM reservoir guarantees the correct material resistance to brake fluid, precise mounting points, and a leak-proof seal, which are crucial for brake system safety and reliability.