I have a 960 and recently faced this exact problem. I bought an O2 sensor and was going to tackle it. It didn't look too terribly difficult just a bit of a pain making sure all the lines got routed back to their original positions in the proper wire looms. There is a special tool for the O2 sensor. You can buy one from IPD. In the final analysis I was having some other work done and the mechanic convinced me to let them do it. My line of reasoning usually go something like: if I'm down under the car with my arm jammed up into the problem and I think, "would I have paid someone $50 to $100 to have kept me out of this position and these problems". If the answer's yes then I'm off to the independent mech. I still have kids at home and golf to play so my time under cars is somewhat limited. It's not a difficulty problem, it's a time/money decision.