It could be just lowering the water to the point below the edge, but I had something similar and the water was dripping from the filter to the rim, I think was where the brace attached.
A bubbler could be splashing water to the edge.
JBWELD Marine is okay for a tank and can be used wet, I had to patch my plastic pond liner a few times with it.
As for the Silicone, check to be sure I think it was GE silicone 1 it HAS to be the kind without mildew additive. The actual fish tank type I found at the local big box too. Yay.