Looking at buying a 2012 RS5 with just over 100,000 kays on the clock. No modifications apart from muffler and paint. Regularly serviced, dealer purchase. Anything to be aware of at that age and mileage?

If it's a DSG transmission, check for at least 1 DSG service carried out and on test drive make sure there's no strange noises from the trans when selecting gears, especially shifting from D to P or from R to P. Might be more to check, but this would be key.
There are also some good videos on youtube lately on what to look out for when buying a specific car.