[SoCal LS-L]

If youre OBD-I its unlikely a moderately failing sensor will throw a code anyways, but theres a few reasons one bank could be shown to be running rich, one of which is a faulty O2 sensor reading.

If you do end up replacing it, I would really recommend spraying the thread connection generously with quality penetrating oil a few times..... as far ahead as you can, at least a day before. Threaded connections on exhaust are a PITA if you dont let them soak beforehand.