Thread right below this one ( at time of posting ) seems to indicate through many people posting, that the valve seat, if OEM from factory, should have potentially been a recall. As they are defective to the point to where it feels like quitting on that day, your engine is also heading to the junk yard in the sky.
Well I just called the ford dealership here where I live and the mechanic said it can be avoided by taking good car of your engine
Im guessing the mechanic wants your business, in the form of parts from Ford, and labor through Ford. Guaranteeing a price tag larger then the current value of the car.
Potential Solution: rebuild head or buy rebuilt head with updated parts / hardware to be certain your focus will NOT give you and your location junk yard quality time together. ( Sorry just got done watching George Carlin Videos, no ill intent is intended )