Sometimes, once the original gaskets along with the diaphragm are soaked in denatured alcohol, they can be removed and reused. If they cannot be reused then I use replacements of the same thickness and width that are made from rubber with a high durometer. When I rebuild I at least disassemble to the point of desoldering the spider from the needle arm and removing it so I can completely clean the diaphragm. But it is sometimes necessary to remove the spider from the diaphragm if it is damaged.
Check this out: http://www.victrolaguy.com/dev1/venues/phonographs/VictorOrthophonic/Orthoph onicNo5.htm Walt Sommers Gettysburg Antique Phonographs 717-334-0862
