Genuine OEM Audi Brake Fluid Reservoir, part number 3D0611301B. This component is responsible for storing the hydraulic brake fluid, ensuring a continuous and adequate supply to the master cylinder for proper braking system operation. It is typically located under the hood, connected to the master cylinder. Made from durable, translucent plastic with a yellow cap, it allows for easy fluid level inspection and is designed specifically for DOT 4 brake fluid. Using a genuine OEM reservoir guarantees chemical compatibility with brake fluid, a leak-proof seal, and correct mounting points, which are critical for brake system reliability and safety.