X2 post #13, comparison to another car is how you develop logic that gets you a diagnosis paid for that shows nothing wrong.
Look at bottom of fuel tank, if caved in more than one inch out of flat the tank is deforming. Then tell the dealership the same thing and that doesn't cost $150. Problem being until dealership knows from the diagnosis the tank is going bad they are free to charge to check for it as many will insist on free checks that then show no problem yet.
You can always try to deal with them to say I'll pay for the diagnosis and if it shows the problem is there you don't bill me for it. If not I'll pay it. You simply can't expect to load the dealer up with non-paying work with no guarantee even of warranty money from Ford corporate if the diagnosis shows no problem yet and it may very well do that. Why they worked it out the way they did. They expect to be paid for anything up to the dead proof of defective product and the diagnosis is a pre-reveal action.
Go for the software flash like said, that will firm the issue up some.
If I had one and the valves went bad that fast at that price I'd be grafting a non-OEM valve in there somehow, not rocket science and many valves will not give trouble like that. It may even be a mounting location thing based on height and fuel level in a full tank and easy to fix but Ford will not go there as they have to stick to OEM fixes. For sure I would not be filling the tank up all the way, that seems to push the problem off a cliff. For example, I had one of the early cars that changed the reliable EGR pressure sensor location to one that failed the parts in as often as 30K miles, I mounted mine higher after two fails in a couple months and the problem disappeared now for many years using same sensor. They had lowered the sensor to begin with just to save on rubber hose. Then it began to show a bunch of fails and even better, more repeat paying work. They will be loathe to fix things like that, the company viewpoint is not what it was in the '60s where you fix a problem to not ever show again. Now they fix it to have you come back again to fix again and double or triple the money.