I had one do me like this about a month ago. It was the fuel pump in my case. I took it off and held it upside down with the weap hole facing up, filled weap hole with solvent and it sucked it right in, it would loose prime intermittently, maybe two times a week just like you describe. The pump was $140 at freightliner.
Good Evening Chris,
Very interesting. Were you making oil, fuel in the oil? I presume that the injector was the source of air in the system letting fuel run back to tanks.