I just finished soldering one of mine. My Dad taught me to use Muriatic Acid the kind that you can clean pools with. He gave me a couple of zinc canning jar lids that you cut up small little pieces and put in the small amount of acid that you will use to clean the spot where the leak is. The zinc will bubble in the acid so you keep adding small pieces until the bubbles subside. I used a knife, sand paper, small wire brushes to get it as clean as I could then used the mixture of acid with a acid brush to clean the area. I use flux and solder that you would use to solder copper plumbing pipes. As stated do not heat excessively as to not unsolder other areas. I use a Bernzomatic propane torch. I have unsoldered the tank tops off a couple of radiators in the past so that I could clean out the tubes, then soldered the tops back on. It is all learning experiance! Also stay down wind of the acid!
