Wanna reduce the chance of rust buildup around the birth mark area (rear wheel well flanges) on 4th gens? There are rubber/plastic liners (not body colored, they will be blackish gray like the mud flaps; and not the wheel well linder, they are just thin strips of material that run along the very outer edge of the rear wheel wells), just go ahead and rip those off, they do more damage than good. They're there to prevent nicks and scratches from pebbels and sand that may be kicked up from the tires towards the out edges, but what happens is, if you live in an area where it snows, and salt is thrown on the streets, that salt collects above the liner in between it and the body, and that is one of, and probably the main reason why rust is common on that part of the car.