If I'm understanding this correctly, the concrete boxes serve as the drop inlet that loads your drainpipe which goes through the dam. And the water is entering the system on the water side of the dam and exiting through the pipe at the backside of the dam? If that's the case and the leak is where the pipe/box connection was not adequately sealed, I don't think the leak will increase over time. It would have to be eroding concrete or hydraulic cement for the flow to increase.
If this is the situation, the big question then is, does the leak in your system exceed the inflow into your pond (stream, spring, runoff, etc.)? If it exceeds your inflow, the pond will never fill. If not, then I don't think you have a problem.
