After restoring players for over 50 years, I prefer leather, or plain
cork gaskets.  I find the cork-rubber mixture gaskets can be a big
problem because often the rubber particles (that are mixed in with
the cork) harden and will not allow the surfaces to seat properly.

In lengthy gaskets, I not only use leather or cork, but I seal the
joint with a narrow strip of rubber pneumatic cloth glued to the seam,
using hot glue.  The rubber cloth, can be removed easily if necessary,
and being rubber will expand and contract when the wood absorbs or
looses moisture.  Drastic variances in humidity are the biggest cause
of problems.

Bruce Clark