In my experience, the sealing of the pressure side of the case is
done by the lid alone.  I have never seen a separate paper sheet.
Sealing round the edges is done by thin leather strips.

There is also an annular leather seal around the central shaft which
should be packed so it is under a small degree of pressure when the
lid is affixed.  It should be lubricated with tallow.

Nicholas Simons, GB