I've given the FAQs a thorough reading. Bearing in mind your (Tony's) comment that the 'component' in the photo is designed to leak a little when repressurised, I should be looking elsewhere for signs of leakage.
The PRV seems OK as there is no sign of any water around the outside 'overflow' pipe.
In the old house where I live, the pipework is mostly underfloor, and ripping up the floorboards would be a real chore. I am therefore eager to ascertain whether the presumed 'leak' is in the boiler itself or in the pipework.
From the FAQs comes this suggestion:
"Get the pressure up to 1.5 bar then shut the central heating isolator valves (both of them) where the central heating pipes go into the boiler, then wait. If the pressure doesn’t drop then you know the leak is somewhere on your system, if it does drop then the fault is in the boiler."
That makes sense to me, but I would appreciate a professional's opinion on the safety aspects of shutting the CH isolator valves - presumably with everything else switched 'off'. And would it do the trick?