I may have found the fix. It has worked for the past 2 weeks. Leave the headlight selector switch to the "ON" position. My theory is that this provides a small amount of power to the ballast (that everyone says is going bad) at all times.
My light (or ballast) issue has been going on for at least 2 years. Service guy can never isolate or create the condition.
I have a 2008 RL that I'm experiencing the same issue. Dealer said 1300 to replace due to the electrical components not functioning and due to the HID yada yada yada. Not paying that for a light. I will try the ON switch.