The two sensors are little black boxes with a little arm sticking out of the side. At the end of the arm, there is a ball/socket type joint to another little arm that is connected to the suspension.
Mine failed its last but one MoT for non-operation of auto levelling on my HIDs because the ball/socket joint had split. The fix was a cable tie wrapped around the joint to hold the ball in the socket. Passed this years and still fine. The sensors appear to be fairly robust, it's the moving joints that fail through wear. They have no protection from grime.
As they are right underneath, I'd suggest a trip to a local fast fit garage and ask them to do any of their free checks that involve getting the car on a ramp. Then have a look underneath while you are there. A few cable ties and a sharp knife in a pocket could see the issue fixed, probably free.