1994 Honda Del Sol Overheat with a leak coming from under t

Hi, My 94 Civic Del Sol has been overheating during regular day to day driving (ie. In traffic, driving arround town, at red lights.) I added more coolant to the radiator to replace the lost coolant and each time I drive coolant leaks out from underneath the cap, I looked at the radiator cap and the rubber sealer looks to be in good condition. At the neck of the radiator right below where the cap screws in there is a small recession that looks almost like a piece of an o ring is missing but then there is a small hole that looks as if it goes to the line that feeds into the top of the resovoir. So im not sure if a sealer is missing or not. I let the engine run for a bit and the coolant defnitely leaks from under the radiator cap. I've heard a couple of different theories about what it might be. It could be that I just needed to bleed the coolant properly, Ive also heard that it could also be that my head gasket needs to be replaced. Or is it that I just need a new radiator cap and or radiator? I got a new Radiator cap to replace the old one that was broken and the same fluid leaked from underneath on the way home.