Power steering control module failure

I have seen similar threads on this topic, but am having trouble believing my dealership's diagnosis. While driving my 2011 Volt home recently on a two lane highway, my power steering went out and I got the "Service Power Steering" message on the dash. While difficult to steer, I continued home (about 15 miles). I charged the car overnight and called the dealer in the morning. When I drove to the dealer, the steering worked fine, but I still wanted the dealer to check things out.

After several days of trying to diagnose the problem, they determined the steering gear mechanism was not getting power due to an intermittent failure in the control module. Their plan is to replace the control module.

When I mentioned there was a bulletin extending the warranty on the power steering to 10 years, their response was that was for the gear/motor mechanism, not for the control module. So whenever they get this done, I will be paying the full amount. Seems to me, and from what I've read on this forum, the mechanical and electrical pieces are interrelated, and all of it should be covered by the 10 year warranty.

Is the dealer correct? Or should I push back?