question about o2 sensors and oil

[kenton]

i got a question....on this car (96 z24), before i owned it, they decieded to put on headers, a test pipe, and some shitty ass rattle can that they called a muffler. so when these rocket scientists did this work themselves, they decided to leave out the rear o2 sensor. so with this in mind, would the back o2 sensor not being there have anything to do with the car burning oil and getting worse gas milage or would that be completly unrelated? it seems to have fouled a plug or two today so i have to get this shit figured out or i am one screwed mo fo! i am hoping that it would be anything other than rings to replace but i am thinking im not that lucky. any suggestions??
thanks for all the help guys!

[4dr92cavi4cyl]

Yeah, they run the hell out of it and burnt the rings, or the valve seals may be leaking. If it blows a little smoke when rolling it's the rings, if it blows a lot when you pull out it's the valve seals. I'm not a rocket scientitst but that's what I've heard.