Before you order up that ignition cylinder, I'd recommend two things first. There is a bunch of interaction between the shift lock override and the ignition switch/cylinder assembly. They are connected with a cable. Be sure that the shift lock override button is absolutely in its "up" position. Tends to get sticky with coffee, crumbs, etc. Also be sure that the button inside the shifter itself fully returns. Secondly, it is very simple to remove the electrical portion of the ignition switch once the plastic covers are taken off from behind the steering wheel. This makes diagnosis straightforward, as you can see exactly what is happening.