Mine's a 2002 which I believe is a facelift model, what are the differences then?
As far as I can see so far (and I am talking specifically S6 here, although I am sure most bits apply to the regular A6 as well. I am guessing that all RS6's are effectively facelift due to when they started production)
- Headlights (at least the xenons) are slightly different - projectors are a slightly different shape, although having tried both, I cant see any performance improvement on the newer ones
- Badging for the S6 is updated, from the older 'RS2' style audi sport badges to the the later style on front, back, kick trims in doors, steering wheel & dials
- metal trim rings round dials, and in the case of the S6, the S6 badge (as well as being the newer style badge) on dials is moved from rev counter to speedo (or the other way round, I cant remember!)
- My early S6 has a straightforward tiptronic box and shifter, with no sport setting (I believe it is effectively always in sport setting, as performance is same as facelift ones, so I assume my MPG suffers instead!) whereas the facelift has a sport setting on the shifter as well as the regular settings.
- Steering wheel is different, with reshaped tiptronic buttons
- I think that the avant rear lights are an updated look (as with facelift 8L A3s) but as far as I know, still fit the same
- I believe that all facelift C5s got the chromed, equal width to top grille, lower middle bumper grille (if you see what I mean!) whereas prior to facelift, only the S6 had this
- I also believe that there is a minor change in where the split between painted and unpainted sections are on the bumpers (I think that facelifts have more paint, less plastic) - Either bumper should fit either age, just a slight modernisation in looks
- From doing a few jobs, there seems to be minor differences in some internal components, although nothing I have found so far that wouldn't be interchangeable (i.e slightly different fastenings for wires etc) - again, this could be due to both being S6's though, and possibly lower volumes of components made, so suppliers changed mid-production etc.
- Rear number plate surround/fog lights bit changes from crappy slightly see-through black on early to gloss black on facelift
This is no means exhaustive, and as I say is a bit S6 specific, as it is fluke that I have a pre facelift and facelift model both on the drive (albeit 1 in far worse shape than the other!!) and also the facelift is an avant and the pre-facelift a saloon, so there are some differences there (such as rear lights) anyway
I would imagine that most parts will be interchangeable - Having worked with automotive suppliers in the past, and taken various VAG cars apart for years, manufacturers tend to be reluctant (unless forced to for technical reasons) to change fixing points etc as it just makes ongoing repairs etc more difficult, and involves re-tooling other components that may not be being facelifted (i.e having to retool the bumper/rad support if they change where the bumper actually fixes on, when this is unseen anyway) which is a waste of money for a small aesthetic improvement.
Dan