Yes the diaphragm is leaking, perhaps cracked with age.
The good news is most regulators seem to operate ~ 45 psig so you should be able to lay hands on one at a car parts store.
If it's not leaking too bad you might be able to get home by just putting a hose on the nipple and running into a container, don't block it off, that would cause over pressure to the injectors.
BTW some earlier manuals show the nipple connected to the manifold, I think at one time the regulators were set for a lower pressure and the connection varied the pressure to match manifold pressure. At 45 psig the injectors are operating in what's known as choked flow and not effected by manifold pressure.
The pressure setting is not critical to double the flow you have to square the pressure so even 5 psi makes little difference but I think 45 psi is common regulator setting.
The Efiman document that describes the early fuel injection systems shows it connected to the manifold, ignore that, it must have been a very early idea. Further into the manual they talk about the pump putting out 44 psi (regulator setting)
http://www.dpguzzi.com/efiman.pdf this gives a very good description of the P8 regulator and most of it also applies to the later 15M type
Cheers
Roy
