So I just mocked this up. Below in the picture, use the Graphic Connection to Part, select the part in the tree to the left, select your now showing Custom property in the list on your right.
Thank you Grundey,
I finally made that work. Thanks for sticking with me.
The main step I was missing was that the part file variable has to be both exposed and the file saved before it shows up in the list to pick from.
Durring testing, I tend not to save stuff so I can go back if needed by just dumping the file.
Glad it was just a non-saved file. Thought I was going crazy yesterday....