Our Bonneville had rust that had begun to get fairly widespread by the time we sold it.
The driver's side power window had to be replaced just a month or so before we sold it.
The trunk leaked.
The rear, driver's side seat belt stuck. You would put it on, try to unbuckle it and it would not unbuckle. Usually I slid under it or kept pressing the button until it worked.
Cassette player did not work.
Gear indicator was broken. Reverse was halfway between Park and Reverse and so on and so forth.
Air conditioning went out during ownership.
Our Bonneville was generally very trouble-free. The power window, trunk leak, seat belt and cassette player problems are to be expected with such an old vehicle. We bought it for a good price and it served us well. It certainly never broke down, or overheated. It was fairly fast with the trusty 3800 engine, got fairly good gas mileage for a sedan and drove well, despite a fairly harsh ride near the end, before we got rid of it.
For being an LE, the car had wood trim, power antennae, the aforementioned cassette player (non-working for the better part of our ownership) and several other perks. One notable exception is that models above the LE had a console-shifted automatic, while our LE had a column-shifted automatic.
The end-all reason we sold our car (and subsequently bought an almost-new white Ford Taurus with 16,000 miles) was because the air conditioning had went out, a nearly essential feature in the summer with a 2 1/2 year old baby.
A few other notable things about our Bonneville is that it had the wheels that appear to be like cris-crossing wire wheels. These types of wheels also appear on Grand Prixes. The engine was extremely reliable. The car was, overall, a great deal for us, and, if it wasn't for the air conditioner problem, it would still be parked in our driveway.
Forgot to mention-a kind of quirky incident was that an already loose Pontiac emblem was even more loosened by the car wash, and when my Dad was showing the car to the prospective (and eventual) buyer, the emblem popped right off. I'm sure the rust will continue and problems with eventually continue to appear, but this car will serve its new owner well and will probably run well until the day it is permanently parked.