Thank you for your reply. The car seems to run fine, there is no noticeable performance problem. I am concerned an error code that seems to point to an oxygen sensor, may be really a "upstream problem", like fuel pump weakeness, clogged filter/injector, etc.
I will pursue the dealer inguiry and see if they are certain they can pinpoint the real failure---and not just find myself throwning parts at the car.
I will post back later with the actual coce number invovled.