whirlpool tub

I had a leak in the ceiling below our whirlpool tub and had to open the ceiling to see what was leaking. When I looked up a drip fell from the box on the side of the drain (containing the stopper mechanism). My kids were taking a bath and when they let out the water more water dripped from this same spot. What is the black stuff? Is there any way to fix this? Do I need to replace or clean out? Thank you for any help!