my light is on indicating I replace the rear o2 sensor (downstream) and the knock sensor. if I want to do it myself, what recommendations does anyone have? can a amateur do it? or should I go ahead and spend the $650 they are quoting me? are autozone parts sufficient enough or what? is the bosch oem o2 sensors on their website the ones I am after? if so, I just need one right, since its the rear sensor thats bad,(they say "2 required")? and the knock sensor is out? any suggestions?