BMW 3 Series G20 / G21. M Performance Rear Bumper Diffuser. 51 19 5 A4F 525. This listing is for item number 22 in the diagram. This is a brand new, genuine OE, M performance rear bumper diffuser in carbon fibre to fit 3 Series G20 & G21 LCI models.Please check the pictures, description and part numbers to be sure this is the correct part for your vehicle. Just because the make and model of your vehicle is listed does not necessarily mean it will definitely fit yours.