As an ongoing project I am rebuilding a Standard brand player.
I have been fortunate so far since the piano is in excellent shape,
particularly the leather parts which are almost new-seeming.  (That
includes the primary valve pouches, by the way.)

All gaskets are "fresh" and only needed light rejuvenation.  However,
at this stage I am restoring the pump assembly and am puzzled.  I began
by rebuilding the governor, whose bellows cloth had obviously failed,
and then continued step-by-step to reduce leakage: this included
recovering (in this sequence) the left pump, right pump, left
reservoir, right reservoir.  I checked the "holding time" after each
item was recovered.

The bottom line is: there was no significant change in leakage after
all bellows were recovered.  (Incidentally, I discovered that the
original cloth was oak as well; the rubber was still soft and pliable).
All gaskets are seated, all screws tight, etc., etc.  There are no
audible leaks while checking with a stethoscope.

The thing will only hold suction for 15-18 seconds, which, measured
at the reservoirs, represents roughly 180 cubic inches of volume.
I have my own thoughts about what is still wrong and how to solve it,
but I wanted an expert's opinion.

Can you please give me your wisdom on this problem?

Cheers,
Dave Talcott