It shouldn't leak, unless overheating. Are temperatures getting high, even in winter?
How's the condition of the radiator cap? It could be as simple as replacing that if it's old and doesn't seal correctly. You say you replaced the fluid, might be that opening the cap disturbed the seal if it was old rubber.
Or, in the case of a Jeep I recently worked on, it could be that the radiator is so plugged up that it's overheating and pushing the water out it top. We noticed the tank at the top of the radiator was literally bulging outward.
-Boyo
