Hi, back 20th December I changed,.... or rather Audi changed the starter motor at my request. I had put cables in on each side of the starter solenoids and measured the voltage each time I started the car. As luck had it, it did fail and this time I was measuring the voltage at the furthest down stream to the starter. So I knew I had a voltage out of the last major component. According to Audi if I had a supply to the starter motor and it did not turn, then the diagnostics should register a fault. There was never a fault registered. But according to my fault finding, it was the starter motor. OR I think the solenoid on the starter motor.
Trying to find a new starter is not easy, and in the end although I found one, the logistics of get and returning the old one made Audi not that expensive.
To date it has not fai, but I still have the cables fitted, because I want to give it TIME.
So if you are desperate this is where I would focus
Hope this helps
Cheers
Jez