S 560 SEL 85″ Earth-gaze?

Moin, I wanted to buy a 560 SEL as a kilometer eater. The price is 550€. It is year 85, was converted last year to earth-gaze has 680000km away. Otherwise full-equipment. With my company car an E-270 CDI of 03″, he had at least 240tkm away, I had an accident, follow = Total damage! A new one is ordered just that takes a few months to get there. I have still my car( w210 E-320) but I have always fascinated myself for the old S 560 SEL, u And I finally wanted to buy it. Normally I could get a replacement car immediately, an old passat, but I get mileage if I would drive with my private car, and because the vehicle just so fascinated, I wanted to drive around with it for the next months. Engine is still the original, the carrier rails have been eroded recently, new tires, on the paint no rust, stained blocks also just renewed. The vehicle is 1 hand and has been fas since its manufacture Now my question, is it possible to calculate with power loss due to earth-gaze????? Because of the gas stations I asked myself, on my route (only Autobahjn) there is an Ergadstankstankstelle all 160km. What to pay attention to when buying? And how fast does the 560 SEL drive?? Thanks already in the MFG TIM