Hi Herb,  My first player was a Lindeman with a double-valve Auto
Pneumatic action (sister action to Standard).  It was playing when
I got it but someone had recovered the pneumatics and replaced the
L-board leather gaskets with felt ones.  I had a very similar problem,
but the piano played, with massive leaking which I could not figure
out at that time (about 36 years ago, when I was in college).  It was
very frustrating!

I eventually rebuilt several Standard players for friends that turned
out quite well (although mostly later single-valve models) and then
I realized that the porous felt gaskets were permitting the valves to
lift at rest ever so slightly.  I replace the felt with buckskin leather
and "Voila", what a difference in pumping effort!  I don't know if this
is exactly the problem but porosity in the vacuum channels sure was the
answer to my conundrum . Hope this helps.

David Oppenheim
Savannah, Georgia