What steps are needed before brazing attic a/c copper tubing with a leak?
Since this appears to be a plumbing leak, the fix is to shutoff the water, drain it as best you can, cut out the bad section, and solder in a replacement section. The whole process is maybe a 30 minute job and will be much more permanent than any patch you attempt to apply. A pinhole leak in one place may just be the first sign of the entire section of pipe going bad, so I'd replace everything that's easily accessible and showing signs of corrosion. It would also be good to double check the grounding straps in case poor grounding is accelerating any issues.