Just bought a '91 100; some questions

[Jason Fantus]

Hi, I just joined this list because I bought a used 1991 Audi 100 (non
quattro or turbo) a couple of days ago. Not a bad deal, $3300 with all
options except the winter package (heated seats, etc.) but who cares about
that here in Georgia, hehe. Even had the factory 6-disc changer. With 100k
miles exactly (low mileage for the Atlanta area, hard to find any cars under
150k or so for a decent price). Seems like its in nice shape, see quite a
few new hoses/wires/parts under the hood and the body is perfect. Leather
drivers seat has a LOT of wear in it but that's not my concern :P

The automatic transmission (I've read the list archives, seems as if its
horribly unreliable!) is a bit jerky in city driving as it goes from 2nd to
3rd and then up into 4th (not overly so, but you certainly can feel it.) but
I have read that it is just how it works in this car, especially the 4spd.
tranny. Other than that, only problems I have a question about are:

1. The fuel gage doesn't seem to work. When I bought it the gauge was
working fine, the gas was just in the red!! (common used car dealer stuff.)
So I went and filled it up, worked fine then too. Decide to take a drive to
the nearest mall for some shopping and a longer test drive, and on my way
back (was dark, turned on lights) the car died in the street! Was able to
get it started back and drive home, however. Just kept my foot on the gas a
bit. But after that event the fuel gage sit's right on empty now. Any ideas?
Might be connected to this one :

2. Radio doesn't work. Have also read in the archives that the delta radio
has been known to crap out before. I was able to get it on for about 5
minutes driving to the mall, after putting in the correct radio code
(surprise surprise, a used car that had all books and manuals, no records
though....was a local 1 owner trade at a Honda dealer, and they even tried
to sell it on their overpriced used lot. Didnt sell I suppose so it was
bought by a used dealer about 5 miles down the road.) it shortly turned
itself off. Seems to sound really nice, though, heh.

I think some of the above may be due to the original alternator being in the
car (checked battery, it's good, funky place to put it though!) and reading
some things that say the brushes go south at 100k. Voltmeter is at about 14,
though. The car I had before this (a 1989 Oldsmobile 98 Touring Sedan, same
price range but doesnt compare to this Audi, still a nice car anyways!) had
the alternator die on the road and the same stuff happened (car runs really
quiet, doesnt have as much power as it should, etc.)

There are NO leaks, fluid levels are all good and the fluids look good, too.
Previous owner seems to have done lots of regular maintenance on the car, at
Audi dealerships or just somewhere as all the newer parts are still factory
Audi ones. Electrical problems maybe? or just some unconnected niggles?