You have a marginal failure and there is probably nothing wrong with the car.

Have the car retested. Make sure it is thoroughly warmed up with a half hour of driving including a freeway run.

Take the car to a place that will test it while you wait. DO NOT SHUT OFF THE ENGINE, BUT KEEP THE REVS AT 2000-2500 until they are ready to drive the car into the bay and hook up the test equipment.

Many Merc models will suffer marginal failures unless the converters are very hot, and extended idling before the car is tested can allow the converters to cool down and lose oxidation efficiency.

Did the printout list percent O2?

Duke