There are a few things that you should consider when buying an Audi V8:
First, make sure you have a good, private Audi-Porsche mechanic in your area. If your intention is to have the car serviced by an Audi dealer you should expect spending a lot of money every time you pass the dealeship door. To better understand what that means, call the Audi dealer in your area and ask him how much some of the following repairs would cost:
At 90,000 miles, the timing belt is due for changing. Most likely, the brakes will require changing as well.
If you you have a leakage in the heating unit you are looking at a major job for replacing it. It is unusual for that problem to occur so make sure that the problem is real.
It is a great car but very, very expensive to fix. It is a car that was very advanced technologically but was not backed by the building quality that the present Audi cars have. It is worth owning one if you have a passion for it. If not, it can cause you trouble.
Best of luck!