Don't forget head gasket issues on those 5.4L it common issue from factory defect. It leak oil out head. It no major issue. Just keep pour oil it will last.
I know one guy in Brown City had 00 E250 with almost 400K. He said it been leak for 200K. Use 2 quarts every 2000 miles.
When I want buy I bring flashlight and go under to look at both heads for any wet spot like oil. If none or very tiny wet spot is no big deal. Expedition had old wet oil spot on both side it haven't been leak yet. Knock on wood.