We had a 1989 grand prix back in the olden days. It was about the same drivetrain as your century. Good, comfortable, economical car but I replaced a bunch of parts on it while we had it. Parts were cheap and it was pretty easy to work on.

Change the fluid and filter in the transmission, flush the cooler. Do this soon, very soon.

Brake disks were a little different and didn't turn on a lathe well, better to buy new.

Ignition pickup, crank sensor on back of motor by firewall, no spark.

Fuel injectors lost resistance and shut down computer.

Fuel pressure regulator, memory not clear, maybe surging and cruise control not holding speed.

MAP sensor, over rich blubbering.

Thermostat gasket went out a couple times. Goofy rubber thing.

Heater core, what a *****, behind sheetmetal on firewall. Wouldn't want to do that again.

I had the upper intake manifold off for something, don't remember why.

GM CS alternator is typical US overrated alternator. Don't make it charge a low battery, use a battery charger. Heat kills alternators.

Biggest problem was an uninsured motorist who turned left across lines of traffic, in front of me. End of interest in car, donated to charity.