That's the point of my thread. I was hoping someone here with more direct knowledge/experience in decks and underdecking than myself would be able to advise me.
The whole underdecking works fine except for that beam. That's where the leak is occurring, because the two crews didn't communicate and the beam wasn't properly covered.
Nothing stops the water from entering the deck. The vinyl underdecking system catches the water and uses gutters and downspouts to drain it.
http://www.marylanddeckandshed.com/under-decking.html
It's meant to keep the finished concrete I had poured at ground level dry - and therefore more...
Thanks for the welcome. Here are photos, as requested.
The deck from above:
The caulking attempts on the surface deck boards:
The underdecking, with gutters & downspouts:
THE BACKGROUND:
Earlier this year I hired a highly-rated local company to refurbish my aging second story wooden deck. It's on the large side: 28' x 40'. The project involved replacement wood decking and railing up top, and underdecking below, with the original deck supports and wooden joists...