Everything. Maybe my car was a fluke but everything failed on this car. Particularly all the sensors for the engine. At the end I had to junk it because it was glorified parts car with a new transmission. But I couldn't drive it too well when I got rid of it because the rear axle things wore out and it violently vibrated back and forth. The transmission mounts sank and the overdrive occasionally worked.
In the year I owned it I spent 4000 dollars on all the repair. The previous owner spent 3500 dollars in the few years he owned. It handled okay and was comfy but with this car I just threw and burned money at it. This car is only good if you love it and don't mind spending 2000 dollars a year on it.
The thing that makes these cars great, are how easy they are to work on and maintain.
If you rely on shops to do your work, you WILL overspend on repairs and maintenance. Only those who know their way around a shop as a novice can see the value in these cars.
I have 2 240 GLs, and they both work wonderful and have nearly perfect everything on them. One has 245,000 miles, and the other has 111,000.
All of my repairs have not exceeded 350 bucks in the shop and 130 at home, but I have met many people who were "taken" for lack of a better term by their Volvo mechanic. But clearly if you look online, you can see how ridiculously cheap parts are. Even so, having to fix them is rare for me and I've had 4 Volvos. I have never been broke down or stranded. Even when I got t-boned at 50 mph I drove the car to a safe parking place.