question Zetor 6718 - original air seat "Aerolastic" diaphragm ?

Hello Everyone,
I'm the new kid in town having just acquired a model 6718 serial number 2623 of unknown origin!

My first problem ( and I am sure not my last...!!) is as follows. The diaphram on the air seat is perished and split. Does anyone know where to source a replacement as I definitely can't repair this part!
Also if anyone has any idea of the year of manufacture of my tractor I would be interested to hear from them. ( The seat diaphram has 1972 moulded into it....??) Thanks for all the useful information in the forum, the handbrake discussion has helped me to understand the braking system which I have yet to get working!

The part number for the diaphragm is 41115417 Roy Perfect Ltd will have them in stock his number is 01768885785

Thanks Alan. I'll get onto that right away, I'm afraid I posted the first reply in the wrong place.....I'll get the hang of this eventually!