Cathy,
It was probably stuck on by old varnished oil. Mine was. It was almost glue like. The shuttle carrier can't pivot on the arm as it sits in a grove. All it can do, if things are right, is move a wee bit in and out.
I'll peruse eBay, maybe someone there will have a picture of one.
Or, I'll straighten this one as best I can and see if that makes it work better.
How about a National exploded drawing, that "might" show me what I need to see. I'll look for that too.
Joe