I bought an A4 1.8i on which the gas guage did not work. I found this forum where somebody had posted an item on how to repair the wire to the sender unit inside the tank. (Its here somewhere but I can't find the link).
I did this over a week ago and eberything was fine till New Years Eve when the pipe to the top of the fuel pump broke. It was fualt as I must have put too much strain on it when fixing the guage. I have only had one price for a new pump but that was 160 pounds so beware of that if you do have a go at repairing the sender unit. The other thing is beware of being in the boot (trunk) for too long because of fumes from the petrol.