[boxzilla]

Frodo ~ I agree, its a very personal decision. I replaced my 2 post cat units even though only 1 had thrown a sluggish code. When 1 of my pre-cat units threw a code, about 1 month later, I only replaced the 1 unit. The other pre-cat unit is still going strong.

If you have the $$ to replace all 4 and you are paying someone else to do it for you, then probably makes sense to pay for 1 install and get it done. Since I do my own wrenching, and most times you can find them for sale with free shipping...then why not just replace them as needed? I don't worry about running the car for a week while waiting for them to arrive as they only impede my mileage and pose no serious threat.

I was proactive and did replace my AOS at 70k since I was the second owner and did not have a service history, and feared the negative impact of a failed AOS was more significant than I wanted to experience. ounce of prevention vs. pound of cure scenario.