Audi A6 - 1995 (Computer problems, oil leak...)

Hi all,
My parents have a 1995 Audi A6 with about 150,000 miles on it. Car has definately served its purpose and lasted 8 solid years. Trips to
Florida and Canada, and everything in between.
In the last few years, the car has shown it's age and mileage. Currently, there is a substantial oil leak coming from around the differential area, which Audi says they'll have to remove to even get to. $1000. Then, there is the issue of the computer not working right. (About 6 months ago, the car got wet all the way thru, and somehow the computer got wet. Audi was able to dry it out and reprogram, but they said they didn't know how long it would last.) Now, the car starts and none of the electronics work - speedometer, tach, gas, windows, locks, air conditioning etc, and the car makes an unpleasant loud sound, like something needs a lot of WD 40. It's a bad sound. lol If this sound happens - when none of the electrics work - the car is still driveable, although if you put it out of (P) into a forward gear or reverse and then back to park, a bad grinding noise is heard.
The radio however, still works regardless of the oil leak/electronic/sound/gear grinding issue. :)
Any ideas on what this is? Parents are not exactly in the financial position right now for another new car, but they also don't want to put money into an unreliable machine.
I say retire the poor A6, 150,000 and 8 years is a nice average lifespan.
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