What would you do?

[Crazy Dazz]

I can’t really visualise what you are saying, so not sure how you know it has had this problem from the factory? From the description it sounds obvious (even to me) that it certainly wasn’t changed or checked last service, but beyond that?
Anyhoo, I assume you’re correct. Since you are so far from the dealer currently, and they are by definition a bunch of dodgy, dishonest ****ers, plus you clearly feel so gutted by this, I suggest that you don’t bother phaffing around with that dealer any more.
Get rid of the car, you don’t want to be waiting for it to explode.
Tell them that since the car was defective when they sold it to you, and they have missed several opportunities to rectify the defect, you wish to exercise your rights under the Trade Practices Act to return the car for a FULL refund. Threaten them with a complaint to Ford and ACA, etc. In the end, be willing to accept a GENEROUS offer from them to buy back the car. Take the cash, buy your better half something else.
If they won’t come to the party with said generous offer, take it up with Ford, and if you feel up to it, ACA, they lap up “dodgy dealer” stories like yours.