Slowly getting there on this one. I've updated https://www.openstreetmap.org/relation/295458 as a route_master grouping of the two main variants of the X40.

Should be easier to add minor X40 variations now, as well as the cut-down NX40 between Wallingford and Oxford.

For these stops, it's the last two Oxford-bound X40s of a weekday, and all of the NX40s.