So. A quick chat with the ever helpful Craig reveals that they have only ever stocked black diaphagms. There is however an upgrade for the seal, which now takes the form of a rigid translucent plastic ring. This is a tighter fit than the previous and serves to retain the diaphram even in the event of losing the cap, which has happened apparently.
As this sits on top of the diaphram, under the cap, I can see no way that fluid can contact it, so I don't think this has anything to do with the blacking issue at all. Duncan, could you please clarify what part you upgraded and where to source it?
#Always use Extra Virgin fluid.
