Old Fogey wrote:They can also supply Viton sheet which may be better; any thoughts?
Does the original diaphram have reinforcing in it like the ones you've made up?
Viton would be good I think. It is listed here
http://www.merl-ltd.co.uk/2003_materials/rubber12.shtml "have outstanding resistance to chemical attack by oxidation, by acids and by fuels".
Yes the original diaphram has a fiber core inside it. I can see it around the edges.