I had the same exact issue when I owned my 09 as well. The dealer replaced both left and right tail light assemblies even though it was only the left one that was bad. My SA told me it was a corrosion issue and they were both replaced under warranty per a service bulletin.
As time goes on, this is becoming more of common problem with the led tail lamps. Hopefully people will have some type of warranty coverage left when the tail lights fail since they are expensive to replace.