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How much engine disassembly have they done to verify this?
What brand and grade oil do you use as well as the filter and at what mileage interval do you change the oil?
Question1- There can be minor amounts of damage going un-noticed but while torn down its a good idea to go ahead and address. Most likely you have cam codes like timing out out spec thus inducing the repair.
2- Scarring really will not cause any damage to the engine below the cam and rollers for the valves, thus me wondering why they say a engine is needed. An engine can even continue running with scarring and can run for quite some time. You will begin to notice power loss once it gets really bad.
3- Yes using ford products and ford specified grade will help in preventing failures. Ford stands behind there products stateing they will increase the longevity of the engine.
4- I would change the oil at a 1000 mile interval after this repair
I personally change my 06 F250 V10 oil every 3k, I do this because I drive short trips, 8 miles a day 4 times, which is bad on oil.
I change my wifes 08 escape 2.3L oil every 6k, I do this because she drives the interstate twice a day for 55 miles one wya and hwy miles and long trips are not harsh on oil.