To address one aspect of the Steinway repetition problem where it was described that the hammers would catch on the backchecks and "freeze", one thing you should check is the hammer height. The lower the hammers sit, the less distance there is between the hammer and the back checks so that when a note is played, especially when played lightly, the back check catches the hammer or tail on the way up. If the hammer height checks out then check the back check regulation.
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