As I posted above, there is an oring prone to leaking behind the water manifold (the metal 'splitter') that the uppoer radiator hose feeds into. There is a gasket and oring there that I have had both leak and the oring leak is the haredest to find but looking at it while having someone start and stop the engine will usually let you see the small stream.

The intake manifold MUST come off to replace the thermostat, gasket, knock sensor or other water lines that live under there. Intake gaskets should be replaced if doing that even though they were designed to be reused, they fail easily.