Well I found one leak. It's the join between two fittings just before the water trap.
Here's what all the leak free joints look like...
And in comparison, the leaky joint...Red is the leak point. Blue is ok.
So I've re applied some fresh sealant after cleaning off the old, and refitted. I filled back up to 150psi and I've left it again to see what the pressure is tomorrow. I'm not really too happy with the way I've mounted the water trap to the tank. Reducer from trap > 90deg > reducer into tank, it's all a bit tight so I may pick up two more of the numatics 90deg swivel elbows and run some air line between them.