It's a wood squeak. A loose lyre dowel joint. Or a worn felt bushing, metal on wood., either damper rods in lyre, or a damper wire rubbing on wood (worn bushing). If it's dirt in the leather, clean it. Or possibly the leather has worn through, metal on wood. Corroded springs, but you checked that. The little damper tray return spring, no felt. Pat W rpt
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