Kevin,  I usually use heavy valve leather of some sort, like
0.040" chrome-tanned goat.  I install it with the suede side down.
Glue to the wood valve (paddle) with hot hide glue.  Rough up the
smooth side of the leather first with very light sand papering to
assure good adhesion.  Follow the original way if possible.

As I recall, the leather is cut longer than the paddle length.  The
extended piece is then glued to the top of the reservoir and a piece
a wood screwed down to form the hinge.  You could also use a suede
cowhide packing leather.  Almost any heavy, suede, flexible leather
can be used.

Jim Quashnock