Welcome to the forum. From your description it seems that the leak is from the superheater flue. IMO that will be very difficult to repair. The material will be very dirty from coal firing, it's probably inaccessible and elderly boilers have a tendency to spring more leaks when re-heated for jobs such as this. You don't say, but I assume the boiler is copper with silver-soldered joints.

Sorry to be a Jeremiah.

Hi Ben

My first step would be to soak it in citric acid for a few hours (perhaps overnight depending on concentration) so you can see more clearly what's going on. As Dave said superheaters are generally removable although admittedly my experience is with larger scales so can't say with yours, I'd be surprised if it wasn't removable. After a bath in citric, it should come up like new. Are you a member of a club? if so once cleaned show it to your boiler inspector for an experienced assessment as to what can be done.

Don't condemn it straight away even if the news isn't good from the inspector, a professional boilermaker may still be able to fix it. Talk to someone like Paul Tompkins at Southern Boiler Works Ltd in Devon, if he says it can't be fixed then it can't although you'd be amazed at the state of some boilers which he has rescued.

good luck

Pete.

Try Paul…..he's more approachable than most, probably the best boilermaker out there too, many won't even look at repairs. At least if he says it can't be fixed you know the true facts.

Pete