John, having just finished rebuilding the stack on my Steck grand,
I can relate to your comments, although mine is a later 1928 model
using the round type of seats, I did measure the existing travel as
being real close to 0.045".  The leather facings also looked to be
in good condition.

I too was tempted to leave things alone.  I was told by several people
not to.  You've got the stack taken apart -- restore it now!

You will find that the valve facings are made of pretty thick leather.
I got the thickest valve leather from Columbia that I could, which is
the CGL goatskin at 0.050".  It only took a few shims (use trimmed down
center rail punchings) under the top facing to get the built-up valve
to the right overall dimension.

As a starting point, use the dimension of an existing valve,
face-to-face.  Put this back into the stack, put the top seat back on,
and check clearance.  Adjust as needed to get the 0.035".  Now remove
it and measure it's thickness (face-to-face).  You can now rebuild all
of the valves to this dimension.

When done rebuilding all of the valves, replace the top valve seats,
and check the clearance of each valve for 0.035 to 0.040".  You will
probably have to adjust the shims on a few of the valves.  Bench test
each stack before assembly.  You will find the book pneumatic to be
sluggish if the clearance is too small.  Make any adjustments as
needed.

I just finished installing the unit back into the piano and the
repetition rate is perfect and dynamics are great.  Cross-valves
were used in all of the supplemental action devices, e.g., sustain,
accordion pneumatics, etc.  I used the same clearance for these and
they work just fine.

One more thing about the valve seats.  The lower seats are shellacked
into place.  Do not remove.

I have read that, over time, micro-cracks may appear in the shellac.
What I did was layer some fresh shellac, using a syringe and needle,
on top of the existing shellac, being careful not to get any on the
seats.  In theory, this should fill any voids.

Good luck on your rebuild.

Jim Quashnock