Hey Zak, I can tell you what I know and what my experiences have been. Brazing is an effective way to fill small pin holes and join very thin metal by flowing the braze over it. The difficulty arises when proper adhesion has not been achieved, leaving gaps or small pinholes. That's the keyword here..ADHESION. This is true also for all subsequent coatings used over the repair area. Any stress cracking, pitting or crevice corrosion will allow water and air penetration to corrode the metal. You did sandblast the area before brazing so it should have flowed on nicely. I haven't done any brazing for quite some time now but I have done more than my share. If you can, sandblast the brazed areas again before using any surface treatments. This will texture the braze and aid in the adhesion of the epoxy sealer. You want to remove any surface contaminations. There are many products available to treat the metal before sealing. I use one called Metal Prep by Alchem. After wiping this on, you have to wash it off completely with water. I have been using a non-sanding epoxy primer from PPG (DP90). This protective coating is all you will need until you turn it over to the body shop. Water can't penetrate this primer. The way to avoid problems like you are hearing about is to totally encapsulate the repair area on both sides, so nothing is exposed to air/water. If the brazing job adhered good you should have no problems. I never had any problems with braze and the coatings I used at the time were not as good as what is available today. This is how I would do it. Good Luck!