The FAA is very strict about the newness of the aircraft, and won't allow old parts anywhere near a new machine. When new aircraft are very lightly equipped, it is sometimes a problem to get the "slave" items on and off because the certificate for a new aircraft can be poisoned by old items.
Why? Because the aircraft comes from an approved production system, which describes how the materials are bought, handled, machined, installed and tested. A used component does not come from that system, and so it makes the entire aircraft non-compliant with the approved production method.
Nice to know these rules exist.