I wouldn't pay extra for it, they can worm their way out of anything if they want to.
The dealership my brother works at has a '06 F-450 Powerstroke in the shop (he isn't the one working on it though) It has 70k miles on it and won't build up enough pressure in the high pressure oil system to start when it is warm but starts great cold. On the 6.0 the high pressure oil system actuates the injectors, so without enough pressure they don't do anything. The guy working on it eventually got ahold of Navistar and they are aware of 3 other trucks in the country with the same problem, they said throw whatever you want at it and if you get it fixed let them know what it was so they can tell the other 3. Then Ford sent down a field service engineer came down to decide if it gets a new engine, he saw an aftermarket intake on it and said that it was dusted, engine warrenty voided. Dirt intrusion shouldn't have anything to do with the high pressure oil system when warmed up, and it runs great otherwise... it obviously isn't the problem and they were looking for something to get out of it, if not the intake it could have been the pintle hitch on the back or something else.
So the owner gets to buy a $12k engine should he choose to, plus more than a couple hours to put it in, plus the parts and labor of rebuilding the current high pressure oil system.
And that was the factory warrenty...
Another guy had his extended warrenty on his fried transmission voided due to slightly oversized tires, I don't remember who it was thru but it wasn't Ford. Same thing, it had nothing to do with the problem but was an easy out for the insurance company.
Keep it 110% stock and keep receipts for all maintenance and you might have a chance of getting them to do something major.