There's a small crack in my roof. It is in the gutter (thta what you call it?) about the passenger door. It is bout the size of a flathead screwdriver, and comes out.

What caused this, and how do i fix it?

 

What causes it.
Ford purposely puts something in the channel. I don't know how to describe it, some kind of caulk. You can [feel the difference between the channel and the rest of the body. The channel catches water, holds water more than the rest of the body so, the caulk protects the sheetmetal underneath. What the caulk does not do well is hold together, when it splits so does the paint on top of it.

I don't think the splitting exposes sheetmetal so, I don't plan to do anything about it.

Rather than worry about fixing it, I'd recommend that when it comes time to sell make sure it's to a short person.