Toyota Yaris leaking switch/sensor

Hello leaking switch on a yaris 2012 auto.its transmission fluid 'its only slight but would like to fix it the problem is Toyota won't tell me what it's called or what it does they said they can change it if i leave the car with them.i said could you just tell me as there's only one bolt holding it on I can do it myself' no won't tell me .Will add a photo it's the part with the wires attached.thank you Tony.ps having trouble adding photo.its at the front of the box on the right hand side . Nearside.