Id replace the radiator, ALSO, Some plastic side tank radiators will leak some in the cold weather. A girl I used to date had a mercury sable and for like 5 years it leaked, but by spring, it was not leaking again.

I wont use the leak stops, too cheap of a fix, and that stuff goes into your engine as well, and you want those small spots thru the engine to be open, not closed up. Radiators arent hard to change either. I am sure you can find a write up or video on the net if not thru this site.