I was much more careful about lining up the seams, and again sprayed the seams with sealer before pouring. Unfortunately, my final pour was not a perfect pour, although it was much better. I had a similar 'double seam' effect, which makes me think the mold shifted around the ball or something as I put the rubber bands around or as the plastic solidified. There was also a similar case of a thin shell forming in the same place on the ball. Given more time, I would try the overmolding in the pressure chamber, which might help with forcing more plastic into the top of the mold. The pure plastic ball definitely turned out the best, so that is my "final" ball to submit. I sanded down the funnel, tried to eliminate what little flashing there was, and cleaned it off. The final result is below.