Depending on valve seat material, one need take care to insure that
no salt base tanning products are used in the process.  If valve seats
are metal (brass with plating) or not, or something else which can
corrode, it's a bad combination.

There are some organ supply companies who can provide acid-free valve
leather.  I'm unaware that valve leather needs to be from a specific
"brand" of creature.  I have a personal like for kangaroo leather --
that being it has virtually no hair.  Most other sources for leather
come from hides with ever so many leaks from hair shaft holes.

Tom Binnall
Auburn, Washington