I'm not a mechanic but I do own a '97 S500 with about 100,000 miles. Car runs great and has a slight yellowish discoloration right below the valve covers-right where a small oil leak will show if your valve covers lose their seal. I would guess it's an oil stain if it's in the same area. Your seller probably cleaned the engine prior to putting the car up for sale. If the car passes a pre-purchase inspection- including a code check of pending codes (in case the seller had cleared the codes earlier- some malfunctions like fuel trim issues need multiple consecutive failures to throw the check engine light but will display the failure code on a code checker as "pending" if it's registered a failure but not enough occurrences to illuminate the light.)

Also check the AC system- put a thermometer in the vent and drive around with the AC on full cold and see what it says. Mine reads about 42 degrees.
If it's warm, be careful- these cars are known to have evaporator failures and fixing them is EXPENSIVE!

Overall, the w140 is the nicest car I have ever owned. It WILL need a lot of TLC but it will also reward you with an incredible ride. Again, Just make sure it has a through inspection by a Mercedes guru so you know what your getting your self into.

Good luck!!

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Paul Hansen

1997 S500 (100,000mi)