S6asta

I'm having a issue with my 2007 S6 and I would like to ask for your opinions. After several inspections, it has been determined that coolant is leaving into my engine. Since my coolant started disappearing without any outside leaks, I have driven the car about 2000 miles while about half a gallon of coolant has disappeared into the engine (there have never been any outside leaks of coolant, neither at the coolant tank or anywhere along the outside of the coolant system including the back of the engine). I would like to know what kind of damage to the engine am I looking at since I drove it with coolant in the oil. The oil and coolant in the car at the ones recommended and sold by the Audi dealership.