The aquarium seal worked, on one side. The hacked tank bolts are complicating this, and the other side leaked a little. It gets re-sealed, packed like a bearing, and retested after 48 hours, when it has time to cure.

I also ended up replacing virtually every other part, basically rebuilding the POS toilet from the ground up, and had just that one tank bolt leak. I'd call that progress.

I could call a plumber - easily affordable. I could just go buy a new toilet, no doubt a better one. But that isn't the point...

As an aside, I don't quite understand why my earlier post about rebuilding a toilet got so many hits.