If you are going to buy a used car, the condition of the car is far more important than what type of engine it has.

There's no reason a Mercedes gasoline engine won't go well beyond 150K but it's also possible for any engine to be ruined by abuse and poor maintenance.

If you are a do-it-yourselfer then buying an old Mercedes in good condition might not be so bad but otherwise, these cars can be expensive to fix if you have to pay someone else to do it.

Diesel engines are made more rugged than gasoline engines because of the high compression ratios. In addition, gasoline is a solvent which is more harmful to an engine than diesel fuel. Hence, diesels can truck on forever if properly maintained.