The story so far:
1998 Sienna with 225K miles. Now a backup vehicle. Barely passed CA smog a few months ago (IOW, I expect it to fail next test 2 years hence, the repairs for which may cost more than the vehicle is worth, so for the next 2 years I'm trying to keep it running with minimal $$$ infusion). (Aside: though it uses a little oil, the powertrain feels as strong as when new; it's the various auxiliary systems that are failing...). Ignition lock/keys are NOT "chipped"; we drive it often with a bare-metal (valet?) key.
Last week, while away from home, driver reported being unable to turn ignition key; fortunately someone was able to assist and jiggle the key/steering wheel etc. to get the key to turn, allowing the van to start and be driven.
Watching various Youtube videos, I removed and disassembled the lock cylinder (see photo at AMZN link below: this is what I'm calling "lock cylinder"), removed & discarded the split wafers, tested before reinstalling, then reinstalled. All was well only momentarily, until I turned the key from ACC (where it needed to be positioned to allow the lock cylinder to be inserted with lock-pin on bottom retracted) to lock: at this point the key could not be turned out of the lock position. My theory is there are anti-theft bits inside the lock cylinder and one of them fell out during my disassembly of the lock cylinder.
Ordered a new Beck-Arney Lock Cylinder with 2 keys (37USD)
AMZN said this was definitely the correct part (and subsequent eyeball checking gave no reason to doubt this: AMZN parts compatibility checking has been reliable for me).
While waiting for new part to arrive, used brute-force (Cobalt drill bits) to drill out the old lock cylinder sufficient to allow it to be turned to ACC such that the lock-pin on bottom could be depressed and the lock cylinder assembly removed. Did my best to vacuum out all the metal chips this violence left behind.
New lock cylinder arrived. Used needle-nose pliers to move the tab deep inside the hole with which the lock cylinder mates, such that the latter could be installed with key in the ACC position. Installed new lock cylinder assembly (same way as old one); installed easily, fit seemed correct.
Test: (reattach ground cable to battery) turn ignition key, ... starts just fine! Victory (prematurely) declared.
[next day] driver reports: "it starts fine, but I can't shift it out of Park". Indeed this is true.
Remove and reinstall lock cylinder, but the problem remains. Brake lights are working (this seems to be the primary culprit of spontaneous "can't shift out of Park" problems, so I checked this even though I am fairly sure the problem relates to my lock surgery, not a coincidental fuse-blow in the brake light circuit).
Any ideas or suggestions?