Got my reversing sensors working today, just wanted to share what I have learned.
One image is of the inside of the bumper with the sensor removed. You can see the two ears that need to be bent back and the sensor can be pushed through from the outside. It doesn't twist as there is a pip in the sensor that slides in the gap in the holder.
One of my sensors needed replacement, the other just needed the connector removed and re-connected again. the other image shows the sensor and connecter and the tab that needed to be lifted to take the connector off the sensor.
Actually quite easy when you know how.