I worked on 2000 Samick SIG-50 that had probably the worst case of tight center pins I've ever seen -- half the keys didn't play at all, some of the hammers flange centers were so tight that hammers wouldn't even fall back to rest. Somebody had previously tried to cure the problem by heating the pins (and scorched the hell out of the wood in the process, but that was largely a cosmetic issue). At any rate I could not find any evidence of flaking plating on the pins, in fact I don't think they were plated at all.
To be clear: I don't doubt that there have been pianos with plated pins in the past, which have caused problems. I just don't think that's what's going on with Samicks from this specific era.
IIUC what happened is that the original manufacturing process overcompressed the bushings, to the point where they swelled back up over time. With the normal cycles of playing and moisture transfer from the environment, they eventually swell back up and get so tight that they start abrading the pin significantly. Which of course makes the action center even more sluggish.
Unfortunately I don't think I saved any of the original pins from that job. I do see this problem somewhat often (yay North Texas humidity swings!), so I'll try to do that next time. It's not limited to Samick either, I've seen this pattern on Tianjin-built Young Changs (Bergmann) for example, where again the pins didn't seem to be plated.
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Nathan Monteleone RPT
Fort Worth TX
(817) 675-9494
nbmont@gmail.com------------------------------