Peter Coggins asked about a sustain problem. As it was described, the
pedal is slow to return. That sounds like a valve gapping problem, to
me. If the gap is to short (i.e.. valve travel too short) the pedal will
be slow to return.
Just to be on the safe side, check out how the pedal works manually, too.
Sometimes, the problem is simply individual dampers, and it sounds for
sure like its the entire set.
Also, when you have damper problems like that, you can very easily
mis-diagnose the problem. For example, when the Duo-Art is playing on
soft pedal, it raises the hammers off the keys to a large degree, raising
the keytails up to the damper levers and lightening the weight of the
damper felt. So sometimes, after the damper rail has returned, even
smartly, the lighter dampers with slightly lower damper levers than
others will sing through their damper felt at that time-- even though
they may not have sung when the soft pedal activated at first.