Welcome!
When you say "downsizing" you need to be careful! The current 9-3SS is actually a tiny bit wider than the old 9-5. And only about 7 inches shorter. It's smaller inside but not much smaller on the outside.
There are not too many things to look at on the petrol engined 9-3. The older diesels seem to have trouble with the emissions equipment clogging up.
Our 9-3 Vector is 9 years old this week. It was one of the first batch made and a dealer demonstrator until we bought it. Not had any serious problem, but it's a low mileage car. Dash and door rattles. Slow retracing seat belt. Failed seat heater element. Intermittent door lock and window operation. But all these seem to have been fixed on later cars. Front seats have slight short thigh support.
Some people report weak alternators. The rear brakes wear quicker than you would expect. So do the front tyres. Hirsch springs have improved the ride and handling as well as the tyre wear. Door handles fade.
Manual gearboxes can be stiff. The auto has a manual +/- position. Headlights are set a bit too low at the factory, but can be manually adjusted.
Just check that all the electrical things work.
My wife loves her car. I prefer my 9-5, but since the suspension was softened, lowered and improved with the Hirsch springs, I quite like it too.
