You hit it on the button. If it isn't broke it shouldn't need fixed exept for what has to happen on a monthly, quarterly, semi or annual inspections.
As far as punching flues we started useing a hottsy preashure washer with a tip desighned for cleaning drains to clear pluged tubes.Then only if the tubes were pluged. To clean all the tubes regularly the brick arch has to be removed.
The cost of replacing the delicate arch brick damageged from handling it every month and from getting it wet alown will slow the need to over manage the boiler, and there is no requirement to punch tubes on a monthly inspection.
Pluged tubes will make the boiler difficult to keep hot, but arn't a safety issue. You do want to keep them clear so that the engine will steam well but you don't have to do it out of safety requirements.
On a K36 the very bottom tubes that sit below the arch tipicly are the only ones that get pluged and they can be cleared very easly with a hotsy and the correct tip & hose.
The K36 locomotives are less proned to pluged tubes with proper firing.
The K27 Is a diffrent story. Keeping the tubes clear in it requires more effort by the engine crew and the shop.
jc