I just purchased this beautiful 280 SE. It has 69,000 original miles. When I drove it on the Hwy, it started like skipping or missing? Is it the timing, or fuel problem? Also when A/C was on I could here like a screaching noise. I think it may be a belt. Would I have to replace it or is there a way to lubricate it. I am not a mechanic. I just love MB though. Please advise. This care is in prestine condition. I paid 4K. Is this about right?