A quick update: I sprayed a little WD-40 into the keyhole and it seems to be much smoother now although it still gets pretty rough after the car has been sitting in the sun all day and gotten nice and warm.

I have the service manual as a PDF and operations pertaining to the ignition switch & tumbler are referenced to section 8D, which isn't in my copy. Does anyone have a section 8D they'd be willing to share?