Why not replace the keyframe guide pin with one a few thousandths thicker? Also, the guide pin should be very smooth, highly polished, to minimize future wear. Also, it is not uncommon in the machine world for the harder material (steel) to be worn down by the softer (brass, bronze, even rubber). It works like this: Foreign matter, i.e. dirt and grit, gets into the contact area of the bearing, sometimes via the lubricant. The grit will get imbedded in the surface of the softer material, where it remains to "lap" the surface of the harder metal. Counter-intuitive at first glance, but true. And I have seen this in very high use, low maintenance pianos. - Tom McNeil - Vermont Piano Restorations
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