how do I replace the cylinder and what tool do I need
ignition lock cylinder replacment on 1991 Buick Park Avenue
In addition to basic hand tools, you will need a puller to remove the steering wheel, a lock plate tool to remove and reinstall the lock plate, and a set of torx drivers for some of the fasteners. This is kind of a tricky job on your 1991 Buick Park Avenue because the ignition lock cylinder includes wiring for the anti-theft system. If the lock cylinder is not installed correctly the anti-theft wires may break and the lock cylinder will need to be replaced again.