I dont think roling the lip is the answer to your problem. If all the other wheels sit correctly rolling the fender lip to make the problem wheel have enough clearance wont even put a band-aid on the problem. Its just kind of like saying out of sight out of mind the problem will still be there. In order to check out the bushings youll have to jack up the car and take a look at them and possibly disconnect the mounts so you can have a GOOD look at them. Also with the car jacked up Id bust out the straightedge and a tape measure and see if there is any deviation in the arms. This can result from a pot-hole bending an arm or a curb hit etc. Take a clean white rag and rub the shock see if any fluid gets deposited on it. Measure the amount that the wheel sits from a stationary chassis point and then compare to the other wheels. This will tell you about any offset problems. Another thing you might wanna check out is if your wheels have hubcentric rings on them that the rings are seated properly on the hub. And one last thing if all else turns out fine Id buy a rear camber kit instead of rolling the lip since if its not an offset problem its a camber problem.