Personally, I replaced the key interlock and shift lock solenoids. This was a few years back. Even that, my shifter could move freely w/o any key. Lived like that for a while. Finally dove back in recently and now it only engages when the key is in.
When you remove the shift knob, it exposes this somewhat pointy edge red tip at the end of the shifter. I oriented it in the right direction as I saw in some forums here that I had bookmarked last year. The reason I finally went back in was because I changed out my shift cover panel and I have a new shift knob. Worked like a charm. Now it only shifts with the key in.
Although I think I replaced something else too....brain is a little foggy.