Genuine OEM Volkswagen O-Ring, part number WHT007920. This toroidal seal is used to prevent leakage in the engine's coolant system. It is located at position 3 in the diagram. This O-ring has a diameter of 0.038 m and a thickness of 0.003 m. Genuine OEM O-rings are made from specific rubber compounds designed to withstand engine temperatures and pressures, ensuring a reliable seal and preventing coolant loss.