Okay, here is the story.
After getting the "I don't care, buy the whole rack" story from the local Ford dealer here in Butler, PA; I went to visit my daughter and family in Dumfries, VA. The Ford dealer there, Cowles Parkway Ford, Woodbridge, VA, easily found the part number and ordered it on Monday. By noon on Tuesday, I had the part in my hand for $16.61 shipped from Memphis! (Part number 7T4Z-7855182-AA) I am impressed by their service and attitude.
Bottom line for the initial concern of this thread is that the deflection in the cover does not indicate a problem or weakening. I do think it suggests that the rails are overloaded.
Because I haul two kayaks and two bikes at the same time, I plan to mount a Thule setup that I used on an Explorer beside the current rails. I will post the results.