If you are going to take it to get welded, have them reinforce the welds on the lower mounts on the front of the radiator too. Those are prone to cracking and leaking too. JB weld will definitely not work, too much pressure, and expansion/contraction of the aluminum with heat to hold well. If you do try to solder it yourself, you will need special flux and solder. Aluminum is difficult to solder due to the vast number of variations in alloys and how rapidly it oxidizes which prevents a solid bond. It would definitely be best to take it to a professional welder to have it repaired.
