CEL 0140 O2 sensor bank 1 sensor 2. 1999 A4
 

purchased this a4 2.8 Quattro as a runner during a financial hardship, runs pretty good but does sound like an exhaust leak during acceleration, however passed CO emissions an therefore obtained the above P0140 check engine code, and the service inspection comes on when it's first starts up, but that goes off, cel stays on.
Has 198,000 miles, does that sensor affect or will it affect how it run short or term? Should I fix it, will it damage the car? Is the service inspection just an oil change ? I want the car to last another 14 month or so. Timing belt, water pump and clutch replaced, by last owner.
Any suggestions...