The problem described in yesterday's MMD would make me believe there is
crossing, or runs, in the channel boards.

Most rebuilders do not notice such small things as leaking between
pouches due to porosity in the wood and shellac cracking.  Then there
are certain notes that cross: they play together or one plays and then
with higher pressure the other one plays.  This may also manifest it-
self, not as a note that plays with its neighbor, but as an odd note
that plays by mistake under certain conditions.

There are several places this can show up.  I suspect yours is a double
valve system.  The L-channel board is what I call the board that
connects the secondary pouch to the primary outside valve.  The two-
piece L-channel board has screws that hold it down, and the screw holes
are close to the interior channels in some places.  If the screws have
been removed and reinstalled several times, those countersinks may
compress and wear the wood down, opening the channels to the air or to
each other.

The solution to this is take the L-channel apart and install new
gaskets.  There is also a strip of pneumatic cloth on the back that
must be removed and replaced, since the rubber on that is toast by now
and will leak, if it is not already doing so.  If any channels are
crossing, you may want to line them with brass tubing before you put
the L back together.

Also it is of utmost importance to pour shellac through all the
channels and let it dry overnight.  I put the shellac into one of my
plastic glue bottles with the pointy snout and squeeze some through
each channel.

Also where the screws go through the L-channel into the secondary pouch
board, there are often cracks in the pouch board that allow the air
from one channel to enter the screw hole and then the channel next to
it.  Do _not_ merely put in larger screws, if the screw holes are
stripped, as that makes the problem worse.  If a hole is stripped, you
can drill perpendicular to the hole and almost all the way through the
pouch board from the inside of the board and glue in a hardwood dowel
for the screw to grip.

When I do one of these pouch boards, I look closely for cracks from
screw holes to channel holes and I line the adjacent channels with
brass tubing.  Usually a simple brass nipple driven into the hole will
do the job.

When I look at a pouch board that someone has recovered, I wonder 
whether they poured shellac through the channels and reshellacked the
inside of the pouch wells.  I can tell this by taping up all the holes
on the edge of the board and then opening one.  I put a tracker tube
with a nipple in its end into the hole and blow on that pouch.  I con-
tinue to blow, watching watch the pouches around it.  A board without
sufficient sealing in the channels will inflate the first pouch quick-
ly, but then with continued blowing, you will see the pouch with a
channel nearest that one slowly rise, along with the one on the other
side of it.  I have seen as many as six or more pouches all rise from
pressure into one pouch.  This tells me that I need to do one thing:
remove all the pouches, pour shellac through all the channels, paint
the pouch wells with shellac, and then install new pouches.  Use pipe
cleaners on all channels after pouring the shellac, to make sure the
shellac does not block the channel.

By the way, a word to the wise: replace all the gaskets when you
rebuild this stuff.  Don't depend on old leather gaskets.  Use coro-
prene (cork and neoprene) gasketing or leather that you really know is
airtight for your gasket.  I am seeing lots of new leather gaskets
leaking like sieves these days.  Don't use some old leather jacket you
used to wear.  That leather is too old to last.  Just go to your sup-
plier and get some new leather.  Then test it for cross leakage: clamp
your lips over the edge of the leather and suck, to see if you get much
air through the grain of the leather.

Believe me, I have spent sooooo much time hunting down problems like
those you are having.  I think these procedures will solve your
problem.

Doug L. Bullock