Oh okay, yeah I broke a o2 sensor when installing dps for the first time. If their stuck you have to break them to get them off?with the right tools, patience, and luck it's not so bad. you need a 14mm swivel and 30" of extensions or don't bother trying. plus soaking everything a day before with pb blaster and letting it sit overnight is a good idea. even at that you may break a stud or find a stuck o2 sensor. either one of those will make the job longer and more costly. luckily i only had one stuck o2. cost me ~$330 for a new one from fontana nissan.