I would sweat them, after the heating season ends if you can wait.Originally Posted by Alaska-Ron
You probably need to completely separate and clean the surfaces for the "Just for copper" stuff, and I suspect that you will have to remove ALL of the solder and tinning of the leaky joint. That is a big job; more than required for solder prep.
Get a tinning flux such as Oatey No. 95. Get a flattened can or other metal shield to prevent burning the wood or drywall, and have a supply of water or a hose available to put out the fire that you don't plan to start. You can probably spring the pipe away from the wall a bit.
You will have to remove and clean the joint. Don't try to repair it by just adding solder. You should probalby remove the whole fitting that leaks and do both ends of it at the same time.
You can use lead-tin solder for heating pipes, or you can use the tin-antimony that is used for potable water.
The pipes must be clear of water with no seepage into the area that you are soldering. It is impossible to solder if there is even a continuous drip.