Well after my trip to Rtech, Nick recommended replacing the N75 valve in my Passat.
I duly did so.
But getting the right part out of the VW Dealer was a bit of an exercise!
The impression I got was that the old numbers had been superceded and the new suffixes just depended on which make the car was!
J = Seat, H = VW , K = Audi
Because I asked for a J and was told that was for Seat only and if you really wanted one you will have to go to a Seat dealer!