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A single key on my upright piano keeps playing even after I release it. I've tried tuning the sustain pedal with the screw all the way up to the point where other keys get affected and the pedal won't sustain them anymore, but this specific key still holds the tone.
I've opened the top lid to observe the sustain hammer (I don't know the correct term for it) and it appears to push back at the strings just like the others, except it's probably not pushing strong enough because if I help it a little with my finger, it suppresses the vibrations just fine. There appears to be a screw on the end of it but it's so tight I can't turn it at all, even with the help of tools.
My understanding of the piano mechanism is limited to know where else to look to fix this problem, any advices?