Re: FEC 148

I would suspect not. There rarely is anything that can't be fixed...if you have the money. However, you may reach a point at which it's actually cheaper to build a new one than to fix the one you've got.
Remember, vintage steam engines were designed using a much different set of rules than the set that governs their operation today. How hard will it be, and how many modifications will have to be made to bring a 1920 boiler up to current standards?
Also, (as I was reminded at the outset of a boiler rebuild) you can do a million dollars worth of repairs to a new boiler and actually make it legal, even better than it was when it was built. However, when you're done you still have an OLD boiler. A boiler that, due to its age and the obscelete technology that designed it, will probably need another million in work in fifteen years or whenever your regulating body makes you pull the tubes again. Lets say, however, you spend a little more (or in some cases a little to a lot less) and have someone build you a brand new, ASME all welded pressure vessel out of the newest material. Then, you use a decent boiler treatment and wash the boiler out at regular intervals, and you pull the tubes at the end of fifteen years (or whenever). You still have a virtually new boiler and stick the tubes right back in (after all of the FRA mandated testing, of course).
I suppose the main question is, are you a historic railroad or a "tourist railroad?" Some are a combination of both. If you're a historic railroad, there may be a desire to repair the historic boiler. If you're a tourist railroad and aren't particularly concerned with "historic fabric," why not reboiler if it's economically viable?
Sorry for the long post. It's a topic that interests me--as our historic boilers get older and older, the question seems to be being asked more and more.