I guess I'm just going to leave this leak. If I could pinpoint it's starting point, I'd go for a fix. But I'm afraid it must originate at a very low level. If the level keeps dropping due to evaporation and the leak, with no rain in the immediate future, I'll have an idea where it is.
Until then the leak at the base of the dam will either self seal, or I'll just live with it.

9 yr old pond, 1 ac, 15' deep.
RES, YP, GS, FHM (no longer), HBG (going away), SMB, and HSB (only one seen in 5 yrs) Restocked HSB (2020) Have seen one of these.
I think that's about all I should put in my little pond.
Otter attack in 2023