One extra step I do is to degrease with acetone, then heat the barrels until all of the condensation dries ( as you warm the barrels with a torch, condensation will form). Then, with clean sand paper, and rubber gloves, I resand the surfaces and re wipe down with acetone. In humid climates, steel will absorb a suprising amount of water. That means it is porus and will also hold trace amounts of oil. Maybe it will help.