I agree with Larry and Peter. The 02 sensor change interval of 60K is triggered by emission and emission warranty considerations. The one time change recommendation at 30K miles for early eighties cars got MB off the hook to have to buy O2 sensors for customers before the 50K emission warranty ran out. Interestingly this change was ONLY recommended at 30K miles - NOT EVERY 30K miles. After the initial change at 30K there was no recommendation to change it as PM ever again. This was then replaced by the recommended 60K PM change, which is arbitrary.

02 sensors probaby have more service life than originally envisioned, and I see no need to change them until they fail or cause emissions/fuel economy problems.

You can eavesdrop on the O2 sensor output by pulling the single pin connector under the carpet enough to attache a scope lead, the voltage should swing in a sharp jump between about 0.2 and 0.8 at a with a period of about 0.5 to 2.0 seconds. Test at idle and about 2000 RPM. If it performs to these specs the O2 sensor is very likely okay and does not need replacement.

You can run this test periodically to determine the health of the 02 sensor or if you fail an emission test or notice reduced fuel economy.

Duke