The commonest cause of this problem is a small particle of foreign
matter that's worked its way in between the outer valve facing and
seat.  A possible solution is to remove the top action and give the
corresponding pneumatic a few sharp raps with one finger, with the
hope that the reverse air flow will blow the particle out without it
lodging somewhere else to cause more trouble.

But don't turn the action upside down as then the weight of the valve
will tend to keep the obstruction in place.  If this is indeed the
problem, you will hear a distinct whoosh of air around the valve only
when the offending note is called for.  A torn, leaking or partially
unglued pneumatic can also be at fault.

The same symptom can be caused by a pouch starting to come unglued,
tearing from age weakening of the leather, or having a hole made by
a tiny insect or worm.  Even a pinched or clogged tracker bar tube
can be the culprit.  Aeolian bleeds are usually made of celluloid and
don't work loose.  But that's a possibility with the later brass ones.

As for excessive drag at the tracker bar, that would be exactly the
same even if you were to remove ALL the bleeds!  Try covering the
outlet flange of the roll drive motor and turning it backwards.  If
you can't develop enough suction to indicate adequate airtightness,
the motor may need recovering or have bad slide valves.  Or the brake
pad on the right-hand roll chuck may exert too much pressure or be in
need of lubrication.  But _never_ put too much oil on the brake pad or
ladder chains, as the excess will fly off during reroll and get on some
of the tuning pins, causing them to loosen.

Jeffrey R. Wood