The dealer is approaching this with a shotgun approach. They don’t like diagnosing these security problems so they just replace all the parts to cover their rump. I have to diagnose and fix about twenty of these cases a year. Every once in a while it does take a BCM to fix it, but usually it just takes the ignition lock cylinder/passlock sensor. What happens is after years of turning the key back and forth in the ignition, the lock cylinder becomes worn causing the voltages that the BCM sees to change. If I were you I would go back to local mechanic and ask him to install new lock cylinder and relearn security. These lock cylinders are no brainers to install. The total job should cost around 300.00.