I have a 2004 G35 coupe. Recently is seems one of the Speedometer backlight bulbs is not working correctly. The lower left quadrant of the Speedo (0-mph) is dim... like a bulb is out. Everything else on dashboard is lit properly. That said, when I go over a bump the light comes on and stays on. It might stay on for entire 20 mile drive...shut car off with it still on... restart car and bulb is out. Sometimes when I restart the car the light is out again...go over bump and light comes on. Has anyone taken apart the dash and seen what kind of bulbs light up the Speedo? Are these bulbs in our replaceable? Any idea of what problem may be?

Thanks in advance.