I have 60,000 miles on '88M5. Have front end shimmy at about 60-65mph with definite pulsating when braking at higher speeds. My shop says front end is fine but rotors are warped. I drive car about 3M per year. Do I really need 7 series rotors or will stock set do ok? If 7 series rotors are used which brake pads do I use? Thanks for any help for this tech challenged owner!