Gutted by CarrG's misfortune, I do believe we need to list Audi UK dealers who are doing either a GOOD job and/or more importantly, a BAD job.
I'll start with the CarrG's experience and recently posted photograph (that I hope he'll not mind me re-posting) as it appears lost in the 'brake-squeal' posts and needs to be exposed:
Not that it helps but it looks like paint. Oil or brake fluid would have soaked into the leather and appear like a 'damp' patch: you've got colour, and that's sitting on top of the leather - looks like paint to me...
CarrG, you have my sincere sympathies, and shame on the Audi Dealership that caused the damage and then allowed the car to be released back to the customer in that state.
The RS3: a great car being spoilt by incompetents.