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I have a Bennett-Bretz player piano with a Standard player action.  The
piano had been working great, but recently is having some trouble.
There are five keys that are no longer playing, although you can hear
the hammers attempting to play.  Also two adjacent tracker holes are
playing the same note: when using the tester roll, I find that F# plays
and then, instead of a G, the F# plays again.

I've vacuumed the tracker bar, removed the stack, and checked it.
Everything looks OK.  I don't see any cracks, the lead tubing looks
to be OK as well.  I've removed the front cover over the valves and
cleaned that.  The only thing that I know to do now is remove the
valves controlling the non-working keys, and check them.  Since this
would require breaking the seal, I wonder whether there is something I
should check before doing that?

The player action was restored a few years ago and was working great.
In fact this is the best player piano I've ever seen; you can pump it
with just one foot and the suction is wonderful.

Your help or suggestions would be greatly appreciated.

Michael Lushbaugh