Starting a few months ago, the rear door locks on my 2009 CTS starting acting up. They work about %40 of the time. Based on my research, I'm tempted to blame the actuators but what is confusing is that both rear doors either work or don't work together. In other words, if the rear driver side lock works, then so does the rear passenger side. They either both work, or both don't work. If each door has it's own actuator, how can this be? Could it be something else? Thanks.