Fully Certified Detailer!!
mate you dont really want to be using an ebay special buffer on any car never mind an S3 mate. if we had the car in we could take readings etc on the paint to see what can be worked with but id go
Menz PO106fa first to see what that would do and if it wouldnt shift then id go stronger on it such as 85RD 3.02 and that will get rid of it, you will be surprised at if you use the right product and correct technique then you will get the paint looking spit and span and better than showroom. if you havent used a rotary before then dont use it on the car as there is a good chance of burning through which will require paint. try and get a proffesional or atleast someone who is competent with a rotary mate.
yours is a similar problem i had on a black B7 A4, the owner found marks that he couldnt get rid of but i was able to remove.