coolent leak

[redsoxsstink]

this leak seems to only happen over night when it gets cold. when i leave for school only sometimes i have a wet spot about the size of a dinner plate under the front of my car. the coolant seems to dribble off of the lower radiator support and it doesnt happen when the car is warm or is running. so far ive replaced all the hoses and clamps (with screw clamps, not the spring factory style) and pressure tested it. the pressure test showed the system does lose pressure but very slowly and sometimes not at all. when we did the pressure test we couldn't find the out where the leak was coming from.

the car is a v6 and the radiator was replaced this summer

so my question is, what should i be looking for? is it possible the radiator is leaking again? why is it only leaking when its cold/not running?