This issue has been around for a while, but some technicians are still caught by surprise by it.
In the early 90s, Young Chang changed the supplier of their cast metal action brackets to another company. Rumour has it that nepotism might have been at play. For about 5 years these new brackets were used in all Young Chang grand pianos. The problem is that after a few years, these brackets, that are responsible for keeping all the action parts in their proper alignment, started growing. Cracking and expanding, actually. At first, the piano would seem like it had gone out of regulation, and the dutiful piano technician would come in and re-regulate the piano. But the brackets kept ‘growing’ and subsequent re-regulations lasted months, not years. Eventually the expansion was so great that the piano could no longer be regulated.
What the pianist experiences is a really heavy action that turns into an almost unplayable action that turns into an action that doesn’t work at all.
The solution—replacing the old brackets with new ones that don’t grow—is still available (as long as Young Chang continues to sell replacement brackets). It requires a solid knowledge of things like action spread and geometry to do the repair correctly, and usually takes about a day and a half. Most of that time is spent undoing all the re-regulations that were done in the past and then regulating the action properly. The good news is that it is a permanent repair (they fired the son-in-law) and will restore the piano back to normal. Most owners haven’t had their piano play properly for a few decades and can’t believe the difference. Very rewarding work.