My passenger door lock stopped locking when the key is turned in the driver's side lock. In the past both operated with the key, and I assume that's the normal manner. The passenger door lock can be operated manually, however. I suspect the problem is an electrical component called an actuator, and I find these for sale on eBay. If my diagnosis correct, do I remove the door panel off to find the actuator, assuming that's the problem?

Yes door trim off and look for the part with the electrical loom and wire arm going to it .

If the passenger door unlocks with the console mounted switch, I would look at the micro switch located on the drivers side door lock cylinder.