Rebuilt Thermoquad issue -- It has to be primed before start each time

Cracked bowl then?
There's only supposed to be a few ways out of the bowls; UP the main wells, and UP the pump circuit.
You seem to have them covered.
I suppose you could fill the bowls, and watch for fuel escaping somewhere that it shouldn't be. But it's tricky cuz at 70plus degrees, the fuel flashes away pretty fast. I think I'd try it with solvent,mineral spirits or paint thinner, or even diesel. Yeah diesel; it will leave a tell-tale greasy surface behind. Keep the liquid level to about 1/2"below the top of the bowls, cuz diesel will climb up the sides,by what I think is called capillary action.
So will the other fuels but they will evaporate before climbing over the side. Diesel is way slower to evaporate, so it will climb over if the level is too high, and of course that would give you a false sign. Diesel will also be slower to migrate thru a crack, so give it an hour or so.