Sorry for the delay in replying, I have been on holiday.
The PCV (positive crankcase ventilation valve) is supposed to allow air to be sucked from the valve cover and engine crankcase into the inlet manifolds when the engine is running.
Parts for the PCV are limited and there were different 'types' to choose from.
The OE part number supplied now is 13H5191 - this is a help as it points you to the fact it is an Austin/Morris/Mini part number, therefore also an MG/Austin Healey item. (it also was fitted to Land Rover and Freight Rover in the UK) The MG item is interchangeable as an assy. A whole item is devilishly expensive at GB £40.00 !!!
The diaphragm rubber is offered as a spare part but no more than that - Diaphragm Part No 27H7758. More reasonably priced at under a fiver.
The spring, and plunger are now not serviced as far as I can work out.
I still favour ditching the valve and plugging the manifold.
Route the breather hose from the valve cover into the atmospheric side of the carb air cleaner. ala TR4
Better still - With a long hose, down into the airstream under the car. - You will not be sucking oily air into the engine combustion chambers then.
Cheers
Peter W