Mine will likely rust out before they actually fail, as I've got 25,000 on my nearly 4 year old Cooper. I guess I'll see if they fail in the next twelve years. If not, I'll replace them at 100k. I might go ahead and book it in for it's 100k mile inspection in 2019.

 

I just changed the O2 sensor in my 03 cooper. About $150 for the sensor.

I used the loaner tool program for the sensor wrench. You will need the offset (crow foot) style socket. The hardest part was running the wire.

From the time I bought the parts to the time I took the loaner tools back was about an hour and a half.

I have never done an O2 sensor swap before, but 2.5 hours seems excessive.

 

I thought there were 2 sensors?

 

One in front of the cat for A/F ratio, one behind the cat to make sure the cat is operating.