There is actually no need in asking anyone. There are required inspections and replacements of parts on each plane at regular intervals. Take the flight timetab

There is actually no need in asking anyone. There are required inspections and replacements of parts on each plane at regular intervals. Take the flight timetables, list the planes, calculate a total number of work hours, and you get the number of spare parts required after a given number of days or months. If a grounded plane is the only source of some critical complex part, and you are confident enough there was no smuggling across the border (because you own/control the supply chains), you can guess that it was used that way.