I have not found an answer, but am surprised you have not found an expert as the question is such a general one.
Please close my question - I will look elsewhere.
Car Reg is JB02CAT
I'm aware that 'no cruise control' can be an issue with a cracked hose/leak - I've checked the hose usually at fault - it looks OK
The brake check valve looks OK as do the areas around the O rings.
I've tried sealing all three with tape to cover off any possible leaks - no difference made - gonna grab some carb cleaner and test by listening to rev count.
no OBD codes ......