I have a little over 70k miles on my 95 cobra and I was wondering if you should replace the O2 sensors after a certain mileage interval or just wait untill you start to have problems. I am very anal about maintenance and want to keep the car in tip top shape. My car is running fine now, but I have heard to replace the o2's after 60k. What are some symptoms when they are going bad? Will you notice a large power loss and major fuel consumption if they are going bad? Any comments or advice appreciated.