Inspected the assembly and oil vapor is getting into the inlet manifold. The diaphragm is really a gasket and I can't understand how this arrangement works unless something is missing
That diaphragm is toast! One for the hall of fame.
I was always a bit suspect of the PCV valve but tested mine on a vacuum cleaner over the summer and it does indeed work (i.e. blocks off high vacuum; opens up during partial/low vacuum) - so it's worth a spin. If you don't get on with it then sell it on ebay as they go for £20-30.