Re: Rear Parking Sensors...
My parking sensors were changed when the rear bumper was replaced after some eygit ran into the back of me when I was stationary at the lights.
The original sensors were the same silver colour ass the bumper, slightly recessed, these did play up and sometimes would not work. You would get the beep when selecting reverse, though no detection of objects. If you re-selected reverse, they would come to life sometimes.
The new ones are black and stick out a little and these work all the time.