2004 DT466 oil pressure issue

I have a oil pump question, another tech here at work did a front gear cover reseal on this about a week ago, from what I have been told he did not pack the oil pump with grease when putting it back together, and he couldn't get it to start because it would not build engine oil pressure so in turn it would not produce any ICP pressure. After finding out that the pump should have been packed with grease, him and my foreman decided to overfill it with engine oil until the pump was submersed and then try to start it so it would prime the pump up. It did start and then he drained the oil back down to normal. Customer picked it up and a few days later it wouldn't start, they towed it back in and I'm checking it out, I found that it is again not building any engine oil pressure so the high pressure pump isn't being supplied oil. I'm not very familiar with these so I'm needing some advice on what can cause this problem, I'm not sure if something was assembled wrong or there is a failed check valve of some sort, how the pump stay primed after the initial start? I don't believe the truck had this problem before the repairs were made. Thank you

 

I finally got a chance to check it out, first thing I noticed was oil dripping from the pan plug, and it was loose, this tech is a hack but is the managers pet and he can do no wrong, I pulled the oil pan, the pickup tube gasket was ok and the bolts tight. No cracks or damage to the tube, I pulled the balancer , the convex washer was in the correct place and undamaged, then I noticed one oil pump bolt missing and another backed out about four threads. I checked the remaining bolts and found them barely snug, I am guessing it was creating any suction because it was not tight enough against the cover. The manager wants to reseal the pump and see if it will start, I suggesting replacing the pump since we already have it out but he says no, we'll see I guess.