I just got my sissy bar in and when I went to put the sissy bar on, the right bar will not sit in the hole. It likes it has some sort of insert in the hole.
Don't know what year you have but they were doing some of the sissy bars with a wedge that went on the end of the bar. That is likely what is stuck in your strut. You should be able to get it out.
The newer bars had tapered mounting ends and the collet expanded for the tolerances between the hole and the bar.
Are your bar ends tapered or straight?