I don't see any issue with dumping water onto the manifold. If the seal is in place, water runs off either end, away from the manifold. If the car is parked on a flat surface, water still runs off either end and only a small amount of water could be retained on top of the seal. I think the biggest issue, at least what I've experienced, is the collection of leaves that build up between the seal and the body while the car is parked. They don't blow away with driving, and unless removed by hand, can fall onto the manifold of the V6 or onto the catalytic converter of all models whenever the decklid is opened.