I'd say they're pretty reliable. I have had a bad one, it all depends on how well it's maintained. At that age you'll want to be thorough, a lot of little things could need work. Watch out for the clutch at that age. If it starts to go and isn't replaced quickly it will break the pedal cluster. Also, those rear subframes can be loose due to rust and age. Hard to tell about that without putting it in the air though.
__________________ "I would not know what the spirit of a philosopher might wish more to be than a good dancer."
- Friedrich Nietzsche
1980 635csi Euro . . . Current
1985 535i . . . Soon to be parted out
2001 Subaru Forester . . . DD