Ok, there are some things I dont understand............what do u mean by "reversing sensors"......as far as I know the reverse lamps/rear wiper is controlled by a
reverse switch from the gearbox(+BCU and IDM of course
).......I f u are sure u checked the right fuse(F18) and the motor is good so is the wiper switch then it could be just a wiring issue or even worst something to do with BCU or IDM(tester needed).....the reverse switch is good taking into acount that the reverse lights are operating as u said so is the auxiliary circuits relay coz it's feeding other systems too.
I'd say open
RAVE > electrical library> description and operation> rear wipers and washers and u'll know more.
By the way in my ignorance i dont know what the "REVERSING INDICATOR LIGHT ON THE DASH" is either
....sorry