Sorry, Bondgirl;

I've got no magic wands for leaks. If I did, I'd put it to work locally! I'm chasing leaks myself.

It sounds like you've done the basics. One caution: careful dye testing has to be done with the pump OFF and you moving very, very slowly, to avoid currents. Otherwise, the currents you set up, will obscure the sort of small leaks you may be looking for.

One thing you might want to try: get the pool COMPLETELY algae free, then raise the water above the skimmer, and turn the pump off. Treat the pool with poured-in bleach, while it leaks down. Then, do it again, with the pump on. If it leaks faster or slower WITH the pump, than without, it's likely in the piping.

BTW, did you check the skimmer UNDER the skimmer basket?