DoDI 4151.20 "Depot Maintenance Core Capabilities Determination Process," Enclosure 2, lays out the specific steps of the core calculation, and includes multiple references to inclusion of lower-level DLRs in the calculation. Paragraph E.18.104.22.168, for example states "Add DLH data to applicable WBS categories to account for DLRs that are installed in platforms/weapons systems . . ."
The DoDI could potentially be interpreted in a manner to permit contract repair of the DLRs, however 10 USC 2464 also says the purpose of Core is "to ensure a ready and controlled source of technical competence and resources . . ." If a depot can swap out DLRs from the PEI, but is depending on the contractor for repair of the DLRs, you would have to ask yourself whether an industry source in fact meets the "ready" and "controlled" criteria
There should be an office at MARCORLOGCOM that facilitates the core calculation process for the Marine Corps. Recommend contacting that office for more specific Marine Corps guidance.