I'd keep looking into getting it fixed, myself. Any other used car you get may have issues as well.
Have you seen [link|http://www.audipages.com/usedA8/usedA8items.html|this] list of common things to check on a used A8? If the leaks are similar in your case, it might not be a big deal.
If you think you're going to hang onto it, if you don't have a copy of the Bentley manual for it, you might want to look into it. I bought the CD-ROM version for my VW TDI, but wouldn't recommend it. It requires an activation, and after a HD crash it wouldn't let me reinstall it without calling them (which I haven't done yet). I got the paper version on Amazon (I think).
My Jetta TDI had a slow fuel leak for about a year that the dealer didn't find. I eventually found that the "tandem pump" (a combination fuel pump/vacuum pump hung off the camshaft) was leaking. It was replaced under warranty and my mileage went from 42-44 to about 50 mpg. That leak I was able to see at idle - you might have similar luck in your case (even with an oil leak).
HTH a bit. Good luck! And keep looking into how you can get compensation from Bob.
Cheers,
Scott.