Nice "creepinformation" (as ususal)!
I didn't want to be without a replacement and the original diaphragm looked worn. I ended up shelling out for a complete new pump as I couldn't find a rebuilding kit.
Somehow related... I have a recurrent problem with the fuel pump that looks unrelated to the state of the diaphragm: most of the times, when the bike goes into reserve (2001 640) the pump refuses to prime after I switch the fuel manifold into reserve. I found out that I can make it prime by blowing into the tank's breathing pipe.