there is no such thing as a true oem part, someone in the aftermarket makes it for them.... sometimes an oem part is of better design but 9 times outa 10 your going to get as good or better than oem quality from aftermarket...for tuneup the only brand i would go with is standard motor products. their o2 sensors are of top notch. and as for o2 sensor change...u dont have to change it but it is possible to see an improvment with a new one. they do get lazy ive done scope tests on them and seen the difference myself