After struggling with sealing the balloons, I made sure the o-ring I secured over the neck of the balloon was on the smooth part of the fitting and not on the threads. This worked well as no bubbles were present at the balloons. After spraying all of the seams, rivets and fittings, I found only one leak on the inside corner seam of the left tank.
I cleaned and dried the area, scapped out all of the dried sealant on the outside of the seam, roughed the entire area with scotch bright, cleaned with methylene chloride and then applied a large corner fillet of sealant.
