doesn't really matter what it looks like, just if it works right or not. My drivers side exhaust always had way more black soot on it than the passenger. Ecu gave me a code 33(left o2 sensor), and when I did the heated o2 sensor test, per faq, it failed. So thats how if figured it needed to be replaced, but visually the base was pretty rusty. Just looked worse after I got done with it.