A stubborn leaky toilet

I've almost given up. I have a kohler memoirs elongated toilet which had a phantom flush going on for a while. First, adjusted, no help; then replaced flush valve flapper, nothing; replaced entire flush valve, still no help; replaced tank with other tank from functioning toilet from other room, it still leaks, and the tank that was with the leaking toilet and is now in the other room is fine. Tried food coloring, and water is definitely leaking from the tank into the bowl, but not at the rim only at the siphon jet opening.

Totally confused. Need help badly.

A little more background: we have a knocking noise possibly due to a poorly functioning regulator that may need to be replaced; a downstairs toilet is not leaking, but the water in the bowl seems to be moving somewhat. Could this be a venting problem?

Any ideas, suggestions would be much appreciated as my wife is losing patience with me.

Thanks,
Robert

Leaky siphon jet on my memoirs also.

I'm waiting for my plumber to install my aquia and address it at that time.
new toilet-annoying as hell.