So I acquired a new barrel, looks like 3G. Probably a few years old but unused, still in wrapper. I've been adding water for over a week because it has a slow leak that's not sealing. After several days it stinks of rotten egg sulfur. I added SO2 to the water thinking it would prevent such problems. It's unlikely I will use the barrel because of the leak, but why did this happen? How do I prevent it in future barrels?