There are 4 O2 sensors on the car. 2 upstream, and 2 downstream. Up vs down just refers to before or after catalytic converters. The upstreams are responsible for actual engine management, then downstreams are really just there to make sure the cats are doing their job.
Then you have the banks: bank 1 is driver's side, Bank 2 is passenger. Judging buy your codes, your downstream sensor on the driver's side is bad. Or, the cat could be bad and the sensor is doing it's job. lol But sounds like you've already been to the dealer, and they are saying sensor is bad.
My guess is they're suggesting you replace both of the sensors on Bank 1 (driver's side).
2009 PBM GT
Under the Knife Again
DOD-delete, , Roto-Fab, BLP Ported Intake and Throttle Body, Kooks 1-7/8 long tubes, XForce Varex Catback, ZL1 Converter, Elite E2 Catch Can, HSRK, Camaro Trans Pan/Filter, GXP Brembos, Cold Case Radiator
Breyton GTS-AV Wheels, 6k HIDs, Holden Steering Wheel and Paddle Shifters, Eibach Springs, 35% Tint
Tuned by Day Tuning