Genuine OEM Audi Brake Master Cylinder Fluid Reservoir, part number 4E0611301A. This essential component stores the hydraulic fluid required for the vehicle's braking system. It is typically mounted on top of the brake master cylinder in the engine bay. Constructed from durable plastic, it weighs approximately 0.259 kg and is designed for DOT4 brake fluid. Choosing a genuine OEM reservoir ensures correct fluid capacity, proper sealing, and resistance to corrosive brake fluid, preventing leaks and maintaining braking integrity.