I am a hobbyist/amateur technician and would welcome some advise from the professionals. I recently volunteered (due to budget problems, the school board won't even pay for tunings) to recondition a "studio" piano for the local high school. Upon looking at the action for the first time, I noticed a yellow powder residue distributed over the action. The action was extremely sluggish, but aside from needed hammer filing, regulating, and tuning, it appeared to be in good shape. I questioned the band director about the yellow residue. It turns out that years before, vandals had broken into the school, and among other things, had discharged a dry chemical fire extinguisher inside the piano! I removed the action, cleaned the cabinet, blew out the action with compressed air, polished the capstans and key pins (the powder had caked on to contact points and was not easy to remove), and lubricated the jack tips, etc. Still the action, although much improved, is a bit sluggish. My question is, should I try center pin lubricant, or would the likely presence of residual yellow powder combined with the lubricant make matters worse? Has anyone experienced this? Thanks.
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