It makes most sense for the OEMs to print the spare parts themselves. Because OEMs are the owners of the design of the actual parts and have complete technical specifications for it. They know exactly from a technical standpoint what can be or can’t be done and can qualify the parts as OEM.
OEMs also have the resources (human and capital) to be able to do it. They are also the unique point of convergence for the parts demand and therefore they consolidate volumes and can better invest in the conversion of parts to additive. For that reason, they can select the right part for 3D printing from a business standpoint and build-up easily viable business cases to apply the technology.
But… then the problems start!