Welcome to the forum, you'll find the members on here are a friendly and helpful bunch :)
Id say that Audi should have sorted the syonechop/rust before the sale. I've had a similar issue on one of my other cars (not my a6) and it is being covered under warranty as the paint defect could only have happened at the factory.
Please keep us posted on how you get on. Hopefully Audi will sort this for you :)
Cheers
Steve