Jwwann, a pond won't "seal" on it's own. As the water flows in a leak, it takes soil with it and erodes a larger and larger path. A rock or something may eventually shift from soil loss and plug the leak temporarily, but will eventually make the eroded paths even larger.
Are you finding much soil in the wet areas behind the dam? Your "dirt guy" SHOULD do the repairs on his dime to save his Rep. Unfortunately in Missouri, many dirt guys have so much work they don't care if a few get screwed.
