> The piano plays very weakly, even though the reservoir is
> completely collapsed.

Carl Kehret is seeing a very common problem with his 1978 "Modern"
Aeolian player.  Even with these players being only 20-30 years old,
the pneumatic cloth seems to harden and the vacuum can't close the
pneumatics.  This cloth also binds at the hinges and the pneumatics
can't close properly.  The only remedy for this is to replace the key
pneumatics.

> Are any Standard replacement stacks available?

Not that I know about.  It is best to contact a player technician
and have him replace the pneumatics.

Pete Knobloch