Just replaced two rear Oxygen Sensor for '00 MB E430 with OEM Bosch. Check Engine went off almost every day for more than a month, I have OBD II scanner and I had to clear the code every day. I bought 2 Bosch O2 sensors on line for $100 shipped, went to my trusted mechanic and he charged $40 labor to replace the two rear sensors, the total time is less than 30 minutes so that $40 labor is a little too high, when I was lazy I had him change the oil+filter with my parts he only charge $5 labor. Total cost for two rear sensors is $140, which is not bad for 9.5 years and 100k miles. The car seems to run smoother and quieter, engine seems to respond to the gas pedal faster and according to trip computer the gas mileage is better by about 4-5%. The car has 102.xxx miles, so that the two rear OEM O2 sensors lasted it expected life, the two front sensors are still working but I am looking to buy it when I can find it for cheap, I expect they may fail soon and like to have parts on hand to replace when it failed.