Straightforwards scenario, I hope:

Bought a new injection pump over EBAY, looks straight off the assembly line, was supposedly never installed or used. Installed as per Mercedes manual guidelines. Part IDs match except new pump is CARB compliant (PES 5 MW 55/310 RS 16-1 instead of original PES 5 MW 55/320 RS 16).

Bled and primed fuel system, but am not getting any fuel from line #1. I am getting regular drips from the rest of the lines when I spin the engine over, but #1 remains dry.

Are there any further tests or checks I can perform, other than uninstalling and taking the pump in for a bench test? Would it help to backfill the pump on #1 (using an eyedropper and clean fuel) and retry?

This is on my 83 240D with 617-series 3.0L turbodiesel