Sorry didn't have coffee yet this morning. I misread your post and believed you were saying the leak was in the passenger cabin in the middle of the van and not the front. I am with NDNV. The leak has to be in the windshield seal if you are getting the leak on that front overhead light.
Had the gasket around the window replaced. Apparently it goes from top center, all the way around and meets again at top center. There is an overlap there, it is not solid. As it ages, it shrinks and pulls apart creating a small leak.