Not sure why, how or where but whenever I have taken mine apart there's juice on the outside of the center tube and on top of the bottom deck. I understand how juice gets down the inside of the center tube, the seal piece that comes with the RSST doesn't seal but the other, well that remains a mystery to me. I suspect that's where yours is originating as well, getting down between the tank and tube then once the bottom deck where the tank sits gets enough it leaks out between the tank and base.
Not a clue, another of those mysteries but I'm going to keep watching here and trying the suggestions.