I have a '05 Yukon XL Danelli that my wife drives and loves. The break light 'bar' above the rear hatch does not light, so I went to replace the bulbs. Once I removed the light bar I could not figure out how to gain access to the bulbs, is this a sealed unit that gets replaced or are the individual bulbs replacable? Does anyone have any experience with the bulb replacement? This is a great forum, thanks for your help. Jerry