Unstoppable Coolant Leak

Don't overlook the possibility that the coolant is coming out around the water ports in the timing cover. I've had gaskets deteriorate in that area, and it makes everything wet, which can look like the manifold leaking when it isn't. I'm leaning toward the manifold myself, but just cover all your bases and check the timing cover as well, especially if it was running for a while with no leaks. Even the FelPro gaskets will disintegrate, and the timing covers corrode in that area too.