Yes, mileage can be adjusted. It's stored in an EEPROM within the cluster. It can be read / write in place with a suitable clip and 'tool'

I think you will need to know what IMMO generation you have in the D2 (I'm thinking it's Gen3 ??) and to have PIN's from both your cluster and the replacement cluster for the swap.

Thanks for the reply mattylondon. I'm afraid as a complete layman I didn't really understand it!
So the mileage in a replacement cluster can be corrected to match the old one, that's good news.
This is the cluster that I saw on eBay:
http://www.ebay.co.uk/itm/1119945436...%3AMEBIDX%3AIT
Can I just plug this in and it'll work??

I had in my mind that the instrument cluster in the FL D2's has the immobiliser chip built into it as well so I think it may well be an issue to just swap a cluster over

I've swapped a cluster on a B5 S4 before but I think it was IMMO1 (1999 plate car with analogue clock), also changed the mileage which involved converting the current to KMH first. This was easy enough once I'd managed to get the Security Key Code (SKC) from each unit.

If the immobiliser chip is in the cluster is it not a matter of then coding the existing keys in or more complicated than that?

I'm afraid not, no.

I just searched the factory repair manual as I'm unfamiliar with the D2, but it did confirm that from Feb 1999 the A8 has a Gen 3 Immobiliser which is within the dash panel.

You see the engine ECU, dash panel / immobiliser and keys are all paired together. Once one is removed it will not work in another car unless it's been adapted.

I've attached a print out from the WSM and do read the below link and watch the video's as the end.

https://sites.google.com/site/imnuts/

Ok thanks very much indeed for the links, that's very helpful! :-)

I had my cluster replaced about a year ago. I got it done at an Audi dealership, as they have to code in the keys. I wasn't worried about getting the mileage changed as the one I managed to source from our sponsors was quite near my own, as I just arranged to take the car in when mine had got to around the same mileage as the donor one.

The simplest way would be to remove memory chip that stores mileage and key information from the old cluster and solder it into replacement cluster

I haven't seen inside a D2 instrument cluster, but wouldn't it be possible to just swap the circuit boards?

OR .... if there's nothing else wrong with the original cluster, maybe just swap the LCDs?

I have not had any issues with D2 cluster so don't know details as well but in my experience with other models LCD is either soldered or bonded directly to PCB or ribbon cable is bonded to LCD and other end soldered to PCB so swapping PCB would be at least as complicated as swapping EEPROM on PCB's.

In addition to this it's not always LCD that is faulty, it could be connection cable or dry solder joints for controller chip or the chip itself. Considering that issue is heat related I would be leaning more towards controller chip dry solder joints which would mean using old PCB would retain the issue. Basically solder joints under the chip has cracked and while cold still pressed together and making connection but as it heats up and different materials expand at different rates cracks open up and loose connection.