My rear center-left sensor is apparently broken, its giving me constant beeps always when backing up. Its coming up as "short to plus" - fault. Has anyone had to replace one? Are the ebay sensors ok to go for? And does anyone know the part number for it, there seems to be a couple of different kind of sensors available and not sure which one to go for. I dont like to remove the bumber first just to check what kind of sensor it is... thanks.