OK, I see a bit better now. This piece appears to be what is holding the seam together. I can see rivets on the top part of it, and some other rivets below the part that pokes out.
So the item I suggested would no fit at all.
Why not just clean up and perhaps even polish the metal part we can see, then mask it with that blue tape, and finally bring your paint line right up to it? You could even do a nice caulking around it, maybe.
Failing that, I think you would have to find some plastic trim similar to whatever was on that metal ridge before. Quite frankly, I have never seen that type of seam in an AS before.
“Courage is being scared to death, but saddling up anyway.”