Wouldn't have noticed except the factory sunroof on my 07 Silverado (Crew Cab, Long Bed Duramax) stuck open in the 'tilt' position (it would still slide open & shut-- but not seal down shut) a couple of times. Close inspection showed serious looking cracks in the plastic covered rails on both sides of roof.

Mine is still under warranty-- when I showed it to the dealership they noted that it had freed up & was working 'OK' at the time I brought it in-- these folks at Jim Stutzman's Chevrolet in Winchester, VA are terrific people & when the service rep saw the cracks she had the whole thing rebuilt & repaired at no charge.

Take time to look yours over, especially if it will be going out of warranty soon!!