it was a little of everything , sealer was drying to hard, and they were trying out a new type base, From what I was told by the GM chemists it was inbetween a lacquer/ water borne type base , the clear didnt have enough UV protection either.
The UV's went right through the clear and attacked the sealer and then the base let go.

GM was cought behind the 8 ball as their lacquer was their big selling point, and every other Auto manufactuer was using Base Clear. So GM tried to go Base Clear fast , with no R&D.
And it ended up costing them Billions !