Change the box fuel filter element at engine.

Do all of the glow plugs work, prechamber diesels need good glow plugs? Ohm each one out or use a clamp on amp meter to test.

An electric fuel pump near the tank does wonders for injection pumps / systems that bleed down. The ones that look like an inline fuel filter work fine. Wire it through an pressure switch that looks at oil pressure so the pump does not run if engine stalls.

Use a manual button so you can run the pump to prime the system before cranking.

I'm pretty sure these pumps ( Stanadyne / Roosa-Master ) have a problem with a plastic ring breaking affecting injection timing. There also might be a cold timing advance system to assist in cold starts.