have him look at this area (from E46fanatics), if that circled area is wet with oil, its your OFHG (you have to take the airbox out to check this). did your mechanic change the 15 grommet seals for the bolts on the valve cover? If he reused them, they could be leaking as well, I'd change them:

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2018 Ram 2500 6.7L Cummins 68RFE
19k miles -Bright White/Black - Big Horn Sport - Crew Cab Short Bed
2013 X5 35D (CEO's) - Born on 5/17/2013 -
82k miles - Alpine White/Cinnamon Brown/Premium Pkg, Sport Activity/Premium Pkg and Sound/20" Style 214/Running Boards