Hi Paul,
Just a bit of advice from somebody who had to deal with the infamous ZF4HP24 transmission: go get a second hand with a low mileage and replace the old one. Do shop arround since prices vary a lot. Changing to a manual transmission doesn't make too much sense if you consider all the additional costs.With an automatic (or automatik) you still have a fine car. On the other hand, you will never turn it into a 2.7 RS, even if you get a chip from Intel. Remember, this was the first charge that Audi took at Mercedes and BMW. It was 1988 and it took them about 10 years to match them. I still drive my V8 and I still think that the technology was not matched (at that time) by quality. That's why on warm days I drive my 1976 MB 300D.
Best regards,
Florin (the only car that I was able to
drive@235 km/h was my Audi V8, I didn't have the money for faster cars).