There are many things that could take the 463 out of service. The one that comes to mind is the flue time rule. As the 463 was restored to operation before the "new" FRA rules went into effect it was not required to have a form 4 boiler evalution done to determine boiler plate thickness. There is also the 1472 day rule that requires a complete inspection of the boiler and running gear, with all necessary repairs. IIRC it was flue time that took her out of service, as it would run out during the winter layover.