If you put any oil in that void you have created a large problem for whoever is going to reblue it in the future. It will migrate through pin holes in the solder and create a mess for the next guy, been there had to deal with that. Plug the weep hole or holes with shot, and if you have leaks, when you are done pull the shot and heat the barrels with a heat gun to evaporate the water. If the barrels were properly tinned, and a non corrosive flux used the barrels will be protected in that void. MKII
