Are you sure it's a 2000? As far as I know the 1st-gen stopped production in 1999 and the 2nd-gen didn't show up at the dealership until 2001.
I don't have an Aurora but the 4.0 V8 version is the sister of the Cadillac Northstar V8. Has tons of power but it is also affected by the headgasket issue. Overtime the bolts pull out from the block (it's aluminum) and it'll need to be re-threaded and use bigger bolts. This happens quite often but no one has statistics on the actual percentage of failure. You can use GM's coolant tab if you have a minor coolant leak as long as it isn't leaking into your cylinders. I have a 98 Deville with the Northstar and I know all about that problem although it didn't happen to me (knock on wood). A headgasket repair job is fairly expensive (minimum of $1500) and a lot of shops don't like to work on them because they don't know how to do it properly and it'll overheat again. They share the same chassis as the Pontiac Bonneville/Cadillac Seville and Buick Park Avenue.
I wouldn't buy it if it's over $3000 unless it has really low mileage and perfect body. If the location of the alternator is the same as a Northstar then the alternator is... under your car.
Oh and the Northstar and the Aurora 4.0 is some of the very few engines that needs to be driven hard, like at least one pedal to the metal exercise a week. Otherwise it'll build up carbon really fast and kill it (and that's why old folks often end up with dead N* Caddies). First you'll hear what sounds like a rod/bearing knock which is actually carbon rap, you clean that out by giving it hell. If you don't then it'll eventually kill the engine.