Dave, I think the recipe thus far has been the seekleak polymer continuing to build and compound within the leak with each application. The combination of the various other materials (clay, sand, gravel, kitty litter, bentonite) were primarily to get anything to lodge in the hole to slow the water long enough to have polymer bond to long enough to set up and begin expanding.
Did you ever pump down any nylon netting? (There are hundreds of different sizes and strengths of grid type products for other uses.)
I would think some netting lying flat against the flow, OR balled up in a restriction, might provide some substrate for your other materials to get bound up into the leak.
