got B1B48-01 left rear outer sensor code. and constant dinging when i back up. it has been coming on and off over last year. seems to be agitated by water/ salt ..

where/ what is best sensor to buy? can you replace the left outer without removing the bumper cover? i think i can weasel my hand in there.
is there any known wiring rub locations on the rear bumper harness that could be it ? or is it usually just the sensor ?