elJefino's comment about the bottom hose connectors having 2 sections is correct. I've push the hose all the way in to the first section and the clamp is in the middle, no room for wiggle.
Shannow, I'm not sure if I understand your suggestion. You said that the different rate of thermal expansion makes the coolant leak through the hose? But the hose is rubber and has clamp that forces it down, regardless of temperature. If you are saying that it is the seal between top of the tank and the cooling fin portion, then I think it is probably not. The whole radiator is soldered from top to bottom and it doesn't seems like there is a plastic seal on it.
Remember guys, I think this leak has been there since I have this radiator new some 70k miles ago, gradually I have to refill the overflow tank at least twice a year. The head is rebuild last year due to overheating when the cooling fan relay went out in a traffic jam in the heat storm. And the coolant hoses (top, bottom, and the one from the block to the heater core) are all newly installed 4 months ago, to this radiator.
I took these photos in the garage with a flash camera after I started the engine for about 1 minutes, and the flash really helps me see where I couldn't see (green coolants and the contrast of the wet belly pan). Every time after I drive the car for about 1 hours and slow down, I can smell burnt rubber around the car and in the cabinet. I ask my friend who rebuild at least 3 of his family cars in the past, and he told me it smells like coolant. BTW, I have a leaking oil pan gasket so it may not be accurate to use smell to detect what is leaking.
