My car was acting up last fall and i never got around to looking at it until now. it was extremely rich on bank one, O2mV's were low and my wideband would read 10:1 (lowest it goes, installed in driver's side of Y-pipe). the car would bog down and cut out. bank 1 fuel trims were crazy as well. it did this somewhat randomly and when i put in a open loop tune it ran ok, but not perfect.

I put new plugs in it.
I've switched O2 sensors side to side, problem stayed on bank 1.
I switched bank 1 and bank 2 injectors, problem stayed on bank 1.
I sprayed carb cleaner around the intake at idle, no changes in rpm.
I found a small exhaust leak at the header collector/Y-pipe joint, shown in picture below.

Would this cause a false lean condition? i mean with the leak close to, although downstream from, the O2 sensor?