im aware this is an old thread but i recently had the problem on my 06 pontiac grand prix gxp and it weaking badly. The drain hoses were backing up and it was leaking on the seal around the inside of the sun roof. The way that i fixed it was used compressed air in the drain tubes then took and put a very nice coating of weather resistant silicone around the entire thing especially the areas that were leaking. Its rained several times since i did this and i have not had a problem with the leaking anymore.
