I have been to Audi Newcastle this morning and picked up the new sensor, part 5Q0906207B. I have fitted it and both the restricted servo and start/stop dash warnings have gone. I haven't had a chance to drive the car since but fingers crossed my issue is now resolved.
Whilst speaking to the guy who works in the dealership Parts department he said they keep stock of the sensors and are selling multiple units a month. He even said he recognised the part number when I quoted it over the phone and instantly knew which part it was which is a statement in itself. He said it is a known issue but not considered common. If each dealership is selling multiple units a month on cars that are still relatively young, and especially considering the cost of ABS repairs if not resolved swiftly, I would say that is a common issue that needs more attention from Audi. The guy also said they have a car in their shop at the moment getting the ABS repairs as the car was driven after the initial restricted servo warning came on. So that is another fellow Audi driver who is about to take a large hit to their wallet for an avoidable problem. Shame on Audi!