Brand new rebuild, oil leak

Just giving some options without making any judgments. I can't see what the owner sees. As my father used to say, "hope for the best but prepare for the worst."
As I and others stated, hopefully the repair shop stands by their work and will correct the issue, if there is one.

 

Steam clean and locate source of leaks first.

 

Another example of why I don't like Cat motors.
I've already been through this, this summer with a headgasket

 

That's not a headgasket area. It's a 2 part value cover gasket. Cheap easy to fix

 

Thats not a leak, its a minor seep

 

That's good news. That's a valve cover gasket and is an easy fix that you can do yourself. Fix it yourself or get it fixed and Keep truckin!

 

I'd make sure bolts are tight. Very likely you find threads damaged in valve cover base. Torque spec is 13 +/- 2 lb/ft.

 

That’s definitely a valve cover issue and definitely not a leak but a seep.
Definitely do as @spsauerland has suggested but a lot of times you will get seeps when something has either sat for a while or you move from colder climates to warmer climates or vise versa.
Also not sure what the issue was with the Cummins shop?
The local Cummins shop here is the only one in the area with a dyno and they can dyno any manufacturer giving hp and torque numbers along with blow by numbers.