I'm sure some A6 diesel owners will already know this but in case you don't: when the time comes to re-fill your AdBlue tank, don't waste your money paying your Audi dealer for it (around £2 a litre!) or buying it off the internet. Cheapest & most convenient method is simply head to any fuel station which has adblue pumps. Costs less than £1 per litre and the nozzle (at least at BP stations) easily fits the AdBlue tank on the A6 C8. Filled up at my local BP station last night for less than £15 and took about 30 secs. Job done