You guys are both more expert than I am, so just throwing out a "belt and suspenders" idea.
If you already have a diver working, could you also add a piece of pond liner?
I am just imagining a 2x2' piece of pond liner to be installed after completing the cement repairs. Apply mastic and place liner. Drill four holes and then install stainless steel masonry anchors with large washers.
If your cement starts to leak again in a few years, the pond liner may stop or minimize the leak. The water pressure at depth would even work to your advantage, pressing the liner down.
Good luck on your repair!
