Seat Mii Wing Mirrors Available Here. Wing mirrors are critical safety features; they let you see what’s in your blind spots when driving. It is illegal to drive without a driver-side mirror, and you can receive an MOT or NCT failure if either or both of your wing mirrors are not functioning properly. If one of your mirrors breaks, you may not need to replace the whole thing. Component parts are inexpensive and an easy DIY project to fit. Replacement mirror glasses on a backing plate clip directly into the housing. There are even stick-on replacement glasses; the stick mirror backing adheres to your existing backing plate. Mirror covers can also be purchased seperately for most models. Some are supplied in primer, ready to paint and some come in black plastic. Be sure to read our Wing Mirrors Buying Guide that includes tips, photos and a video.