2014 Volvo VNL D13 long starts

1.1 million miles on the old girl. Was planning on using it sparingly to haul grain. Seems to be loosing prime and can take 10 seconds of cranking before it starts. Starting Fluid does seem to help, but not every time.
I just changed the fuel filter and water separator on the Davco system with no help. Still has the same symptoms.
I don't have a computer to check fuel pressure so when I replaced the filter I did turn it over to see how quickly the fuel came out and was shocked how little cam out of the filter housing with 3 seconds of crank time. I am suspecting the fuel pump, but once it starts it runs great. Ran it 6 hours to get it home, then 5 minutes after running it looses prime and takes forever to start again. Looking for suggestions on where to go next? Pump, relief valve, or are we suspecting an injector issue. No check engine lights even after long crank times. Seems to run good once its going.
Thanks!

 

Is there replaceable O rings or did you replace the entire housing?