Open your hood and look down into the engine cavity.
See the aluminum heat shield on the front of the engine?
The O2 sensor is down on the right side of that heat shield, screwed into the exhaust pipe. It looks just like a spark plug with wires coming out of it.
Both the oil filler cap and filter are on the opposite side of the engine. Only the worse mechanic in the world, would ever slop oil on that sensor.
I can't even imagine how that would ever happen.
Even I'm not that big of a Klutz.
I've had my oil changed twice so far, , both times at the Suzuki dealer and have had NO problem with my Check Engine light, or any light coming on.
O2 sensors are good for about 60,000 miles. After that they begin to drift out of calibration, due to contaminants in the gasoline. They will cause the engine to run richer and richer as they continue to age.
Contaminated gas can cause premature failure of an O2 sensor.
A black sooty deposit in your tail pipe will tell you the engine is running rich.
I always change my O2 sensors by 60k just for safety, and for the best efficiency of the engine. Today, gasoline is too expensive to be just blowing it out your tail pipe.