Check engine - Oxygen Sensor 99 SL

[99SL5]

I have a 99 SL500 with 47k miles. Last weekend I filled up at a small town Mobil station. On the pump it said their gas is oxygenated. I am not sure if this has anything to do with my CEL coming on but I thought I would mention it. After using a quarter tank the CEL came on. The OBD code was P0150 (Oxygen sensor bank 2 sensor 1). It seems to be running fine. I have removed and retightened the gas cap with no luck. I erased the code. Is it safe to say that if the light does not come back on everything is OK? Should I replace the driver side O2 sensor before the manifold? Does anyone know how to do this? Is it difficult? Is it bad to drive the car with a bad sensor?

Thanks