2006 RX400H Ignition Cylinder Issues - Car Won't Lock

[MissCesium]

I have a 2006 Lexus RX400h, which has in the past had that classic "key won't turn in ignition" issue, which was fixed when a tow truck guy gave it some percussive maintenance. Well, I've run into something new. Normally, when you turn the car off, but leave the keys in the ignition, you cannot lock the car from the doors in order to prevent you from locking your keys in your car. Well, I turn the car off, take the key out of the cylinder, try to lock the car, and the same result happens, i.e. the car is behaving as if the key is still in the cylinder. Other than this, the ignition is fully functional, no turning issues (currently), starts up and shuts down fine.....except I can't lock it. Which is an issue. I took it to the dealership, they suggested a replacement of the ignition cylinder assembly, for which they would charge $945. I am competent enough at fixing things that I could perform a switch of the ignition cylinder itself, as demonstrated in various places on the internet.

HOWEVER, because I'm not sure of the precise origin of this issue (did a wire get crossed in the cylinder to keep the circuit open permanently? is there a part of the cylinder assembly that governs this function that is not part of the core tumbler?), I am unsure if I could eliminate the issue properly. Has anyone else had/heard of this issue, and if so, what resolved it? Is there anyone on here with sufficiently detailed technical knowledge to explain how this door lock prevention system works and where the failure might be located?

Thanks in advance!