Ignition switch problem

Currently I am unable to turn my ignition switch to the rear in the ACC position in my 1987 Buick GN. It works fine starting the car. Any ideas how to fix or what the problem is? Thanks!

GM ignition switch tumblers tend to wear out over time. You can probably crutch the problem by buying some dry graphite lube and squirting it in there, but replacing the whole assembly is the only true fix. Its not too tough... it involves purchasing a new ignition cylinder which can be installed by removing the steering wheel and turn signal assemblies.

The whole mechanism is made of brass and some soft steel. Over time it wears out and becomes sloppy.

Thanks! I found a "do it yourself repair guide" at Autozone.com and it looks simple enough.