So I took off a plastic disconnect and attached a barbed stainless one. I ran out of hose clamps so a press fit over the barb was holding it on.
The stainless disconnect appeared to have solved the problem as there was no HP needle movement over 24 hours. However, after 36 hours it had moved. F%^k me. Here we go again. This bloody bush league hose-barb and shitty ball valve manifold is next on my hit list. Leaks through valve stems I've seen before.
Hell, the leak's slow enough that we could even be talking diffusion through the vinyl hose.
I am going to run a parallel line which is 100% Festo pneumatic components into a SS disconnect which is pushfit >> FFL thread. If this leaks then I'll give up and resign myself to the fact that excruciatingly slow leaks are reality in a non-welded system.