BF230FT easy to start when cold, but hard to start when warm.

I pressure checked the fuel system. Engine off, I jumped the fuel pump relay to run the main pump. System immediately pressured up to 43.5psi (300KPa) as manual says it should. I checked the fuel pressure regulator by drawing a vacuum on it, and the fuel pressure dropped proportionately. I then deactivated the main pump and pressure immediately dropped to zero. Not good. Manual says it shouldn't go below 20 psi in 20 minutes.

I next disconnected the injector manifold (fuel log) at rubber hosed feed-line to pressure test fuel log, injectors, and fuel pressure regulator with air. No leaks and pressure regulator bleeds pressure when at 43.5+ psi like it should. So the leak is somewhere prior to the engine.

Could the pressure loss on pump shut-down is through a check valve? The arrangement looks like the main pump pushes fuel through a short fitting that could be a check valve, then the fuel filter, then to the engine bay, and then through the fuel log.

One more thing. The pre-pump pressure also drops to zero when it is deactivated (10 psi when operating). Is that a problem?

Can anyone confirm a check valve might be the problem? It's location? It’s replacement? Should Teflon tape be used to seal threads?

Thanks for the attention!