After reading comments from Don Teach and Spencer Chase about making
gaskets for the Ampico A block unit valve, I thought I could offer
a simple solution.  Bob Streicher makes high quality die cut gaskets
for these valves.  The material is cork.

Using leather for these valve gaskets may create problems.  If the
leather creates any corrosion in the adjacent screw studs that mount
the valves, it will be a disaster.  These studs are very unique and
extremely difficult to reproduce.  Why take that chance?

If cork gaskets are not what you want, consider using the correct type
of modern cork/rubber composition.  Cork/rubber composition can be
found in a wide variety of qualities.  Some of it is of poor quality.
Some of it will last indefinitely.

Thirty years ago I researched cork/rubber gasket material.  I found
a material that was used to seal natural gas meters.  It is expected to
last as long as the meter it self.  The material was made by Armstrong
and carries the identifier of "DC-100" in 1/16 inch thickness.

The only problem with this material is that it might be too hard.
It is designed to hold up under high torque bolting applications as
one would find in gas meters.  Do a Google search for DC-100 and be
prepared to for lots of data.  It won't be Armstrong, but the DC-100
is the "standard" for many manufactures.

The sponge application on unit valves is okay too if the sponge will
hold up.  Most won't, but sponge rated SC-43 with skin both sides will.
I don't think the self stick type should be recommended as there is no
guarantee what the adhesive will be and how it will behave for years
to come.  It might migrate.

Cork/rubber DC-100 does not take hot glue well.  But the glue will hold
lightly, and final assembly will keep the gasket in place.

Bob Taylor