Could be the heater. It's likely that most of the hoses to the rad were changed, but maybe a hose to a heater (if you have more than one), or the heater itself.
maybe your radiator is broken and you need to get a new one or just get a reparation if the radiator starts leaking when is in use it may be leaking because of the pressure of the water.
needs a new heater core
get a new hose
Remove The Radiator And Take It To a Good Radiator Shop. Most Likely Yours Can Be Cleaned And Repaired. When You Reinstall It, Add New Antifreeze Plus Water Pump Lubricant. This Will Help Stop Corrosion. Good Luck
Blown head gasket?
yes
Replace the radiator with a new or good used one.
It is not normal for antifreeze to be leaking out of a car. Period. At all, no matter what car or where it's leaking from. Try buying a new cap. If that doesn't help, call a mechanic.
have system pressure tested to observe leak
When the current one is leaking or plugged.
If your radiator is leaking then you will need to replace it. Additionally, if you find that your car is constantly running hot you will need a new radiator.
Stop leak is a temporary fix. I don't recommend it. Tighten the clamps on the hoses going into the raditor.