I am a player piano technician in the New York City metropolitan area.
I see _a lot_ of player pianos which are very hard to pedal due to
leakage.  The most common player I "run across" is the post-WW2 Aeolian,
the next most common is older Standard/Autopiano systems, followed then
by miscellaneous older players, Universal systems, etc.

I agree with D. L. Bullock on his assessment of post-war Aeolian player
systems, I just want to add to it.  Although it has inefficiencies --
excessive valve gap, neoprene that warps and hardens, etc. (these
neoprene valves typically leak) -- these systems, valve leakage and
all, are still very compact efficient systems.

I find the most critical thing is the condition of the striker
pneumatics.  If the striker pneumatics are disintegrating and I can
fairly easily poke my finger through them, they _need_ recovering.

I posted recently about my use of "Flex Seal" -- the clear type,
not the messy black stuff.  Unless my customer wants to pay me to
recover pneumatics (which I always tell them is the best way to solve
their problem) I may even offer them another alternative: sealing and
patching where needed.  I seal and patch the bottom bellows, especially
the reservoir.  I tell my customers I can guarantee my work only if
I _recover_ the pneumatics.

When the bottom bellows are removed, I spray Flex Seal on the reservoir
and maybe the feeders as well if they want to use the foot pedals.
I can brush some Flex Seal on the fronts of the striker pneumatics,
where it's most critical.  I tighten the nuts for the machine screws
in the stack that hold the three deck boards together.

There is a slide valve that "governs" the amount of suction to the
stack from the suction box and it is controlled by the opening and
closing of the reservoir.  This valve may have been a big plus when
the player piano was new, perhaps, but it's become a hindrance since.

The quickest and easiest way to make these play better is to loosen
and slide the collar forward and tighten the "set screw/bolt."
I can also seal off and by /pass the soft bass and soft treble valve
pneumatics if they leak and if the customer doesn't care if they work.

I also service lots of Standard player actions.  This winter in New
York it was unusually cold -- my customers turned up the heat and the
relative humidity levels dropped way below 20%.  Many of my customers
double-valve Standard/Autopiano actions stopped working.  I had to pull
out the stacks and tighten 70 or so screws associated with the valves
and pouches.  I also did all my other tricks and got the players up
and running.

I had a customer with an Ampico that looked well rebuilt.  I just
suspect the pouches shrunk due to the dryness, raising the valves off
their seats.  Yes, I tightened the stack bolts as well as screws for
the action cutout primary valve block.  Humidity control is very
important and player piano owners need to know this.

Bill Maguire
New York City