I've had to fix my driver's seat twice. Been told that you can't buy a replacement diaphragm for my model ('97 series 1, manual, non-abs, non-electric seat). Guys at British Offroad on the Sunshine Coast had a second-hand one they sent me - it lasted about 2mths.
I took my old one that had torn (through the rubber) to a conveyor belt service place. They glued some thin rubber over the whole lot (top and bottom), and it's good as new. I reckon it'll last as long as a new one, with the glues those boys use!!!
To get it out, I took my seat out (4 bolts on the corners). The diaphragm has about 4 hooks on each side, that hook into the seat frame. I just used a screwdriver to unhook/rehook them (please a fair amount of grunting and groaning!)...
I used Apex Fenner (closeby), but any company that repairs industrial rubber conveyors will have the good stuff...
Hope this helps!
