On my old derby car radiators, I would fix cracks or all out holes by brazing. My favorite fit all radiator was twisted 4" bottom corner to top corner. It took a hit to where the top nipple was pushed through the front of the tank. It took some doing, but I saved the nipple and fixed the hole in the front of the tank and the cracking around the back side. After squaring the tanks back out in a press, I pressure tested it to 15 psi, and didn't have any leaks. In the case of the side mounts, I would follow Bmorgil's suggestion and soldier the straps back into place with the 50/50 acid core. As far as stainless, you do have to pump argon in the tubing to be successful. I just did a quick and dirty on my headers since I was given the material the night before the run. I wasn't 100 percent certain that the MIG would penetrate enough to be good. The photo above was the prior to the third run with them installed. The heavy wall pipe didn't change color much with the heat cycles.