I'm in the same boat as you are. I have a .62 acre pond that was put in about 1 year ago, when it was dug it had several wet weather springs that were leaking into as they were digging. But they also ran into rock at the bottom and I beleive it is most likly leaking along the rock shelf under the dam. I have found an area behind the dam about 50ft that has water trickling.

It also looses 1/2 inch a day. And with my calculations, for my size pond that is about 5.8 gallons per minute, which i think would be close to the trickle I see below the dam.

Now I have thought of doing some of the things you have done with placing bentonite in areas where I think it is leaking, but have not yet made that leap. For now I will live with it, unless I come arcoss some free bentonite or free dozer work.