Genuine OEM Volkswagen Oil Separator, part number 03D103515B. This part functions to separate oil mist and vapors from the crankcase ventilation system, returning the oil to the engine's oil sump and venting clean gases. It is typically located within or connected to the engine's crankcase ventilation system. Genuine OEM oil separators are designed with precise internal baffling and material specifications to effectively manage oil and air flow, preventing oil consumption and emissions issues.