I have a light out as well. My dealer told me that you need to send the radio in and have it repaired. They need to disassemble the radio to get to the buttons. In other words, it was not worth the trouble. Also, it is not covered under the warrenty.
There were some posts and instructions on this a month or so ago. You have to remove the top shelter and remove all the screws on the bottom of it that hold the two halves together. Then you can extract the radio. You have to seperate the top control unit on the radio from the body of the unit and then you can get to the bulbs from the underside of the circuit card on the control unit.