Over here in the UK we have different brands to those available in
the USA, but I may be able to guide you to a suitable type of product.
Many years ago I was told to seal thin leather with a dilute solution
of Evo-Stik instant and acetone.  The former is a contact adhesive that
used to be and maybe still is rubber based.

Since acetone is hard to find I was advised to use the product known
as 'Dab-It-Off'.  This is a small bottle of instant stain remover,
where the top of the bottle has a wadding to let though only a small
amount at a time.  This liquid may be acetone (certainly smells like
it) but it certainly is a solvent for the Evo-Stik.  Use a ratio of
five parts solvent to one part rubber solution and apply one coat only.

Many player piano people over here recommend Hydrophane Leather
Dressing.  I have tried this and would certainly recommend you _not_ to
use it.  It has a tendency to creep away from the treated area and into
the surrounding wood.  This will make future restoration difficult.
I also think that it softens glues, including traditional animal glues.

An alternative treatment used in the past was egg white.  My own policy
is to seal leather only if it needs sealing.  Not as daft as it sounds!

Best regards from GB,
Nicholas Simons