Here's a little bit of background info on what the SR&RL folks are going through with #3, as well as MNGRR folks are dealing with on #7 and #4.
Way back when, Edaville had new boilers built for all their steam locomotives. I've heard various stories about what boilers were built when, but I think the boilers for 3, 4, and 5 (our #10) were built at the same time by the same people. This would have been late 50s or early 60s. When the boiler builders put in the stay bolts to connect firebox to boilershell, the welders took a shortcut and didn't do their work correctly, leaving gaps in the weld where there should have been solid metal. Over the years, daily use put stress on these boilers.
A few years ago, Boothbay Railway Village got a contract to work on #3's boiler - retubing, originally, but I think a few other repairs as well. One of BRV's shop crew is our own master mechanic, Jason. Jason, and another BRV crew person, Brian, co-own their own business, Maine Locomotive & Machine, which is working on MNG's #7 boiler.
When dismantling #7's firebox, Jason & Brian encountered some strange things with the stay bolts, but it didn't trigger anything in their heads until they encountered the same issues with #3's boiler. Jason, before he had cut anything on one particular stay bolt, was able to snap the bolt off in his hand. This is bad. They called in an ultrasound company, who studied the bolts and discovered bad wasting all over the place. They had MNG's #4 boiler ultrasounded, and found the same thing. Immediately #4's boiler was condemned. We brought the company up here to look at #10's boiler. Evidence of similar wasting in progress was found, but it was within tolerance. If you look at the service histories of these engines, the reason why is obvious: #10 (#5 at Edaville) was operated for only 10 years, at Pleasure Island, and then stored (except for brief usage to generate electricity for Christmases). One of #3 and #4 were used daily for 30+ years, with the other on standby, during the normal season, and both used hard during Christmas season.
So SR&RL was expecting a simple fix, but unexpectedly found themselves in a much deeper hole than they anticipated. The whole point of this story is that you really can't blame them. The good news is, once the firebox is back in from what I've heard the boiler will be good to go for retubing.