[Marshall V. Daut]

I once ordered a very expensive double sealed water pump from a well-known private vendor. It leaked from Day One exactly where your leak apparently originates. No amount of hose clamp tightening or even hose replacement solved the problem. Because it was double-sealed, the packing nut was purely cosmetic and tightening it would have no effect. Nothing worked: drip, drip, drip. Finally, I removed the water pump and examined the casting. It was cracked on the bottom of the mating surface and had come to me that way! I don't know whether this was created by improper boring for sealed bearings or whether it was an original housing that had once frozen and had cracked. Very disappointing. That was the last water pump I ordered from this guy, as I had perceived a drop-off in quality in the last couple I had ordered from him for my cars and for customers.
Anyway, if tightening the clamps and replacing the upper hose don't help, run a bar of soap over the bottom portion of the pump housing where water in the cylinder head rushes past. If the leak temporarily stops, the housing is cracked. Try the other suggestions posted so far first, but keep a cracked housing in the back of your mind, should no recommendation work.
Marshall