Parking Sensors

Evening all, my parking sensors have stopped working. When i go into reverse for the first time i get the usual single tone for a couple of seconds and the flashing light on the sensor button. I done the listen to the sensors whilst the car is in reverse test and found that my front right sensor doesn't 'tick'. So finally my question is, can I replace the sensor without removing the bumper? and just out of curiosity because this is the 3rd time ive had to replace the sensor since April when i got the car (well a garage has), if it isn't a sensor that's causing the problems what else can it be? By the way i just got my car back from the garage tonight after my last parking sensor not working issue. Has the garage just not changed the original !Removed! sensor or am i that unlucky that another sensor goes !Removed! 20 mins after i pick it up?

Any advice/guidance would be greatly appreciated as i am ready to explode