Considering that the initial troubles appear to be too popular (left side AF issue, oil spotting, internal flare, shutter trouble), at least the first six months should be considered as "moratorium", which should elongate the life cycle of a camera.
I decided to by my D750 one and a half year later than its release, and consider it rather well-seasoned than old.
It is interesting that the life cycle of the Canon cameras (except for the entry-level APS-C models) are longer than that of Nikon ones, which can be good for suppressing NAS.