I would definitely buy it if I were you and it was the right price. Here are some things I would check:
Phone cover on dashboard
Oil pressure and Engine Temp
Oil changes. M119 is an engine that likes its oil to be changed alot.
Rust on mufflers
Condition of rotors and tires.
Startup of a M119 motor also tells if it is still tight and tuned. Starts up strong and then it should be as quiet as "an ant pissing on cotton" and idle at a steady 600 rpm with no shaking or vibration.
Doors should vaccum close fast and quiet
Exterior door handles. Some stick open. Back side should be very tight, front doors aren't as taut as the rear ones.
If you get the car take it to a mechanic and have him test the O2 sensors. 75k miles is the maximum amount of mileage I would buy. Unless documentation shows timely service/oil changes. I have a 99 S420 and I believe it has the best interior that MB every made. I also have a W220 S600 but I always get more compliments on the s420. "Damn, this car is like a limo...I feel like Princess Diana." The new s-class is overbearing and common. The 97-99 S-class is the zenith of what a benz is suppose to be. The v8 is excellant but the trans is the real angel. Its shists are unnoticeable when cruising like a CVT but then feels like a F1 gearbox when nailing the throttle.