the interior courtesy lights don't come on when door opens.

Yup, I have check them and replaced one. The body control module on the Passenger side wall bottom connector when loosened can cause a courtesy light to flicker. I wonder if the BCM module is defective. Has there been any history of this module being faulty?

Sure they can be faulty. A lot of different makes and models can have issues with any module.

The issues that I have been having have gotten worse over time. I may remove it an find a replacement.