Help...I just bought a real clean 560 SL from Florida with 103,000 miles. Sometimes the car runs great, real smooth, and then for no reason it starts running rough which seems like a miss to me. I checked the plugs, they're fine, the rotor was a little corroded so I cleaned it up and it ran super for about 50 miles then it started all over again. Anyone have an idea what the problem might be?