I assume your corrosion resulted from the unprofessional refinish that was done by the fellow who drilled that weep hole but didn't know how to purge the moisture before sealing the hole.
Or, since I believe I understand him to say that the hole in the barrel corresponds with the solder-covered weep-hole in the rib, the previous guy may have actually MADE the hole in the barrel while drilling the weep hole. In that case, there might not be a corrosion problem at all. On the other hand, disregard if I misunderstood the situation as it exists.
I had a set of damascus barrels on a GH that I discovered a hole in when I re-finished them. I found it when I kept finding a small leak into the bore after each cleaning. I didn't recognize it for what it was the first couple of times I saw it, then the light came on and the stomach turned. I stripped the ribs expecting to find a mess of corrosion. Instead, I found beautifully clean barrels with a small pinhole that must have been there since it left Meriden. We gas-welded the pinhole (made easier by the fact there was no corrosion), ran a reamer through the bore to clean up the inside of the weld, relayed the ribs, proofed the barrel with the hottest commercially-available loads I could find, refinished the barrels again, and I still shoot it regularly with the standard <7000psi handloads I use for any damascus gun. I didn't trust myself to do the welding for fear that I might distort the barrel diameter. I had a friend who is an expert do it. I told him beforehand that I wouldn't hold him responsible if it didn't work out. He reluctantly agreed, but I knew if he felt the completed job was sound, then it would be safe. I watched and it went incredibly well. The filler metal mixed marvelously with the parent metal, and he was even able to build up a little extra thickness in the area of repair. Best of all, the whole repair is invisible because it is entirely between the ribs. I DO NOT RECOMMEND THIS TO ANYONE, AND TAKE SOLE RESPONSIBILITY FOR MY OWN ACTIONS, but I have shot this gun for three years since the repair and have complete confidence in it. It seems like taboo in this country to weld a hole in a barrel, but the fact is, the English muzzle-loading shotgun crowd consider this a standard repair under the right circumstances. The friend who did the welding has since welded holes in a few of his own projects with good success. Again, I do not recommend this to anyone! You only get one set of hands and eyes.
