Water seeping out the back toe of the dam suggests the dam wasn't cored properly. If that's the case, then the entire pond bottom, and up the sides, needs to have compacted clay. Or, you may able to dig a core trench, backfill, and compact it well into each end of the dam, beyond where the dam ties into the hillsides.

I'd be tempted to dig into the front side slope, above the water level, digging several feet below the water level, and see if these test holes fill with water. If so, you can resolve it with a core trench. Mike Otto wrote a story about digging a core trench after the fact and compacting it with a remote-controlled ditch compactor.

I'd be tempted to call Mike and discuss it with him.

Teach a man to grow fish...
He can teach to catch fish...