Genuine OEM BMW Crankcase Ventilation Oil Return Line, part number 11151745649. This line is a critical component of the crankcase ventilation system, designed to facilitate the return of oil separated from blow-by gases back into the engine crankcase. It is constructed from durable, oil-resistant metal to withstand high temperatures and internal pressure. Genuine OEM lines are essential to ensure the correct routing geometry and secure, leak-free connections required to maintain engine vacuum and prevent oil leaks.