S8 Report and Reliability Question

Four days in the new to me 2002 Audi S8. I'm 54 and have owned a lot of
cars over the years. This is far and away the best sedan I've ever owned.
Put it in Sport mode, and the transmission matches up to the Brembo 13.6s,
the 19 inch wheels, and the stiff suspension to make this a wonderful
performer.

Having said that, it appears that Audi has a "worse than average" reputation
for repairs. This is my first Audi. It has 22,000 miles on it. It was a
lease car in Arizona and has been on the dealer's lot while they adjusted to
the market for 10 months. What should I expect it will need, and what
usually goes wrong with the S8/A8 from 2002?

Last question: Is the Nav system as useless as it seems, and if so, is
there anyway to upgrade without ruining the looks of the car's interior?