Well, by way of a conclusion and feedback to all who helped, thats the valve block fitted with new o rings and diaphragm which was cracked around the metal insert although deceivingly, the crack couldn't be seen till the diaphragm was removed. The link in the thread above by NicP38 is great and made the job a skoosh but thanks for all the positive advice and guidance from everyone thats (so far) made P38 ownership an enjoyable and pretty inexpensive (apart from fuel) experience.