For VWs, it's always the electrical systems.... If it's 10 years old, I can almost guarantee it's going to have problems. With that said, you'll always see the rouge 1999 Jetta tooling around town, and either the owner got really lucky, or they've worked on it.

Sister in law had a ~’04 Jetta. Mechanically it was sound, but it did have a continuous stream of electrical problems. My nephew had an ‘09 CC that blew a fuel pump and then blew up an engine. Nice car otherwise.

The only car we've had that had electrical problems was a Toyota - where the instruments would keep cutting out. Turns out this was caused by the sunroof...

Edit: Sunroof leaked, water collected at lowest point inside car where Toyota had decided to locate electrical connectors that fed the instruments.

As long as they keep it simple they do OK. Audis are rolling wiring harnesses.