It is almost impossible to say where the water you are finding originates. If the water flowing is at a higher point than your current pond level, the pond can't be the source...if below the pond level, it's a total guess, but I'd lean toward it being the pond.
If the pond where mine, and I had good clay on site, I would chase the gravel under the rock shelf on the pool side of the dam, and into the dam as far as I could and back fill with good, compacted clay! Exposed gravel and broken rock shelves are almost guaranteed to leak unless you know for certain they are cut off while digging the dam core...Polymers sound great, but I have yet to hear of any that were anything more than very temporary fixes....
