[alexanderstears]

6 million parts is probably misleading. Bolts, screws, and washers are replaced perfunctory and with aerospace-grade parts that are presumed to be in compliance - half the parts on a plane might be things that are replaced that way.

Also, that part count is probably inclusive of the engines and avionics and those are inspected on separate schedules by separate technicians. Lord knows how many parts are on a 747 circuit board, but as long as the board is working correctly, do you need to check every capacitor on the board?

The D service also takes tens of thousands of hours and months - each panel is removed and every inch of the aircraft is inspected by master technicians and factory representatives. IT can only happen at special factories that have the space for the plane to come apart and come back together like it should.