Sounds like the saga of IRM,s UP 6930 Centennial.
UP had a power shortage in early 1984 and pulled 40 of the DDA40s out of storage for return to service. Cannibalization and repairs brought 15 of them back into service. But with most having over 1.5 Million miles on them only 10 remained in service at the end of the summer.
6930 was one of the 5 removed for mechanical problems. Apparently 6930 is “complete”. However I have herd that many of the parts it has are not properly attached and had been swapped with other units still in operation.
Possibly keeping all the locomotives with a complete set of parts (even if broken) was a requirement for possible sale, or trade in with EMD. Something UP did try to negotiate.
I feel that keeping an artifact complete is job 1 at a Museum. Documenting any removal or swapping when something is needed elsewhere just as important.

I had a 'block of instruction' (AKA class) on BDAR, Battlefield Damage Assessment and Repair, as part of an Army Reserve NCO school I attended 25 years ago. One of the examples given was that of an armor company commander, with two tanks that he could not fight with. One had a failed transmission, the other had a bad fire control computer, which controlled the gun.

The recommended solution there was to take the computer out of the tank with the bad transmission, and put it in the tank that could move and otherwise not fire it's gun. So you wind up with at least one serviceable tank.

The railroads did this all the time. Of course, sometimes with not the best thought out plans, however. A CMO that I knew years ago told me about one of his mechanics that took apart a factory rebuilt Woodward PG governor. He harvested one of the magnet valves to put into another governor that was on a locomotive. The CMO would have rather had the rebuilt governor installed as a complete assembly on that locomotive.

Reading the old issues of Rail & Wire, I know that many Chicago Elevated cars were purchased for parts at IRM. The duplicate car remains were later burned/scrapped.

At WRM, we have an early restoration that has a set of Chicago Elevated seats from one of these cars. they were the best historic seats available at the time. It seems to me that parts trades take place at museums and long before that at the railroads themselves!

Ted Miles, IRM Member