440 Oil Pump Won't Prime

This style of pump is a positive displacement pump,- they don't require "priming", moving parts need lube, but not nec to prime.
Look it up !
Commonest prob is gears installed wrong on assembly, and seizing .
Plugged inlet,
Next is sucking air !

"Most positive displacement pumps do need priming. In order to be self priming the pump must be sealed well enough to pump air. If the pump can remove air from the suction line, the atmosphere will push liquid into the pump."

Difference between a positive and non-positive displacement pump