I had a FF tube installed on my Ar10, and Armalite sent me the new ejection port door rod.
I took it to the smith, and we discovered they sent a standard rod (the same length as was already on it), instead of the longer FF tube rod.
The smith cut out a piece of semi-hard rubber and filled the gap between the rod and ff tube with it (friction fit).
It's worked great for two years.
Armalite did send the right part out, but I had to pay shipping. It's the second time they have sent me the wrong part and made me pay shipping for the right one. I'll take it back in and have the right rod put in some day, but I believe the FF tube has to be removed and it's gonna cost me a box of ammo, so I'll most likely shoot it like this til it fails or just run it with no ejection port door.