The Bilstein B4 Series 44-400187 is a premium Monotube Air Strut designed as a direct OE replacement for the rear left suspension. Engineered to restore the original ride comfort and handling characteristics of your flagship sedan, this unit integrates seamlessly with the vehicle's electronic air suspension system. This is a single unit; for a complete rear axle overhaul, it is recommended to replace struts in pairs. Part Number: 44-400187 (Rear Left).