The problem with John Dewey's friend's piano is that like my own Knabe
Ampico I just sold -- the problem is cumulative.  Over time everything
becomes just a tad weak adding up to an overall system operating with
less than ideal vacuum.

For my yardstick of standards, where I expect a piano to perform
flawlessly, the solution isn't in locating a leak somewhere but a
complete rebuild.  I am sure by fiddling around you can improve it and
fool yourself into thinking you have fixed the problem, but everything
must be very, very tight, as the entire system depends on every
component being perfectly tight.

See what the pump is pulling first.  I have heard that 80 inches of
water is fine, but I won't settle for anything less than pegging the
needle.

Don Winter