If it was brazed vs soldered, your torch wont get it hot enough to remelt the original joint which would be the ideal way to repair. There is no harm in trying however . Use plenty of flux, and have solder handy. When you heat the joint, concentrate the flame on the outer pipe. If you see the joint liquefy, you may be done at that point but you can add a little solder at the top while heating at the bottom (solder will pull around and into the joint on its own if its hot enough and enough flux was used). If you cant get it to liquefy its probably brazed. You can still try using solder, but you will simply be attempting to fill the cracks in the braze that are currently leaking. instead of the solder migrating easily around the joint on its own, you will need to heat and add solder fully around the connection. In either case, keep the chiller still while it cools down. Movement during cool down can cause micro cracks (cold solder joint) and is likely the original cause of your current problem.
