ok.... my downstream o2 after the cat (2k fed spec 5-spd), is gone, meaning sensor not there only wires hanging, my options are oem replacement, o2 sim. what should i do? i am not to familiar with using o2 sims and how good they are or how safe they are. i was given the oem part number for the oem one and i bought it, turns out its the wrong one now they wont take it back although it hasnt even been opened and they are telling me that in order to get the correct one its gonna be $160. the o2 i ended up buying is for a maxima but dont know which one, any suggestions are appreciated. thanx in advance. Ramsey