Back in the days of A and E models, (and I'm assuming little would have changed with the 'H' model), on a long trip, the FE would take away two very large boxes, (as I recall, but am ready to be corrected, the 'A' kit and the 'B' kit), containing a rather large number of parts to replace those likely to go wrong while away.
It was not unusual for the FE to have to replace quite a large number of instruments and other sundry items during the week away on a Vung Tau or Phan Rang service. With the bits from the A and B kit in place of the originals, the aircraft would depart Darwin perfectly serviceable... but arrive in Richmond u/s, with multiple entries in the -500, because the paperwork required by the hapless FE to transfer all those parts from the A or B kit inventory and onto the aircraft inventory was formidable and extremely time-consuming.
So the FE and the co-pilot, (much to the horror of any pax who visited the flight deck for a smoke), usually spent a major part of the cruise between Darwin and Richmond ripping out all the serviceable bits and replacing those that could be replaced while maintaining safe flight with the original u/s bits... which the poor bloody ground crew had to turn around and replace again after the aircraft arrived.
Stipid? Everyone acknowledged it. But apparently, it took less time and work (for the FE at least?
) than leaving the serviceable A and b kit pieces in place.
I'd be willing to bet that something very similar happens with the H model to this day.