Nice to see that it worked out so good for you with the plastic. Altering the shape of the plastic strip instead of the translucency makes it even easier
Looking at the pictures of your control-arm, I see that the factory have tried to change it a little from the earlier model. On my SewQuiet 4000 the arm is just a square piece of steel, while your SewQuiet 5000 at least have a radius on it.
Now itīs time to run and find some plastic....