Sooner or later, we are going to run out of spare parts for preserved diesels, as power units (some of which were still in production until surprisingly recently) and spares go out of production and there are fewer good parts left on donor locos. Smaller components can of course be made easily, however, what will happen when a large diesel engine needs a complete new power unit and none are left available? Will the owning group stuff and mount the loco? Scrap it so her sisters can benefit from her spares? Fit a new power unit of a more modern design which will alter the performance and naturally the sound of the loco? Or as happens with steam locos, reverse engineer the existing part and re-create the original engine? I'd be interested to hear different people's points of view on this matter.