Fuel Starvation, no apparent cause!

Hmm, that sounds odd to me.  I'd have liked to know - specifically - what he actually did to "reseat" it.  

At this point, since the problem began directly after his "fix", I would definitely have a different guy/company take a look at that float valve and all its related components.

If the needle valve seat leakage test is not done when working on problems with leaking past seat there is no way to know if it is correct. The procedure is in the manual, invert carb apply 6psi fuel pressure, needle valve should not open with just the weight of the float arm. I battled with this and finally got a new carb. Old carb would not hold no matter what I tried. New carb passed test. Should not happen on 30 hour carb. Before letting anyone work on carb question should be ask if they do the test if not find some one else to do the work.    

I have replaced the needle valve and the float bracket and the problem persists!

Have you checked for a blockage in the supply hose to the carb?

The fuel pipes from the tank to both carbs have been replaced along with the filter.