Can anyone comment on the 90 degree offset crossbar ends? While it was a very easy fix, I am curious.
The riveted end should rotate freely. The rivet is supposed to go into a groove which encircles the plastic shaft. The screw is supposed to go into a fixed hole, to lock the other end. There should be some Teflon tape inside the aluminum tube around the plastic shaft on both ends; this acts as a lubricant on the rivet end and a spacer on the screw end. You might try squirting some SailKote around the joints to free up the rotation.
My boat originally came with the black tendons, so I bought the retrofit kit to install these elbows. Unfortunately, the instructions had a typo, which would have put the screw and rivet holes in the wrong place to work properly. It's possible whoever assembled yours had those same flawed instructions. If you remove the screw and pull out the plastic piece, you can see how it should go together, and check the hole locations.