Just bought a 2006 TDI S-line Quattro, I was looking at some of the invoices and noticed at about 20k miles an untraceable coolant loss was reported, it's on 65k now and does not lose coolant, so it's safe to say whatever was leaking is now no longer leaking. I suspect it was probably the cylinder head. Will Audi be able to give out this information? failing that where about will I find the code on the cylinder head. Mainly for peace of mind if nothing else.