The check engine light came on and so I had the codes read at Autozone. According to the reader, the O2 sensor on the drivers side cylinder bank before the CAT is showing a fault. They offer the Bosch OE one #15088 and a generic Bosch 15738 (need to use the old O2 wire connector). I looked online and saw another part #C5010-88839 here on fastline which I suspect is the Mercedes part number and so is relatively expensive?

Best prices I found online are 97.95 for #15088 and 79.95 for the #15738, these include free shipping. Anyone know of a better price? Which would you buy?

Other information: The check engine light came on in the past whenever the car went through a car wash (with underbody spray), it would then go out after a day. I suspected that perhaps the cold water was playing havoc with the hot CAT or hot O2 sensor. This time it stayed on longer (few days) after the last car wash with underbody spray and is why I had the codes read. Car engine runs smooth and has 108K miles, but I'm concerned that eh CAT will deteriorate quickly with a malfunctioning O2 sensor.

Thanks, Mark