I had been a chasing a fuel delivery issue with my T595 Daytona since before Xmas and after changing fuel line and filter i was scratching my head as to what the problem was.
Narrowed it down to no fuel getting to fuel rail for injectors and possibility of the fuel valves being blocked or not opening when the lines are re-connected, i removed the fittings from the tank and after trying to blow thru both one had no flow.
Pushing in the one way valve i could see the end of the valve has an o-ring that moves away from the seat allowing fuel flow, on one fitting the o-ring had swollen so even moving off the seat it still blocked the flow of fuel to the rail.
So a measily 8mm OD o-ring was giving me grief and was difficult to diagnose, this must have been an issue for a while as i had been getting some spluttering when revved hard which now seems to have gone .