how often replace the O2 sensor? Not that they are going bad, but is there like a preventative maintenance thing for this?

 

That kinda depends...I have heard every 60,000 miles, but I dunno how accurate that is. I wouldn't really worry about it until you see a big drop in gas mileage or if you are going to install some headers. I have also heard that it is part of a major tuneup as well.