I used a different approach to the the diaphraghm issue. I notice mine would hook inside sometimes on curves.
I cut clear plastic pieces the same shape and size as the striker plate on the diaphragm and glued them on the ends. that way both diaphragms have smooth flat surface to slide on. It worked great for me.
I used a glue that did not mar the surfaces too, so if I want to remove the covers, it can be cleaned off.