Buy it. It's the second best car Audi ever built. Only the saloon is better, as it's lighter and stiffer. Shame they didn't build a 2 door saloon!
Problems:
Yes the original plastic distributor drive gear does shatter. The VAG replacement distributor has a steel gear (why they fitted plastic I don't know). You can't buy a spare gear from VAG, and a new distributor cost a fortune. Check out US 20v web sites, someone was making new steel gears to order.
VAG exhausts cost a fortune, and weigh a tonne.
Like most Audis of that era, the standard brakes aren't good enough. Be prepared to fit ATE power discs or Berembo equivalents (GSF and Europarts) with EBC green stuff or red stuff.
Cracked sumps can't be welded (Mag alloy). New ones cost a fortune.
As it's 1990, it has probably got the welded tubular exhaust manifold. Check it for cracks. Funnily enough, my cast manifold had a crack. I replaced it with a welded one.
Buy it anyway. The sound of the 20v 5 at 7500 rpm is amazing.