Any Plumbers in the Nut House?

It looks as though the eschutchen sleeve may work as the nut aroung the packing,I would turn of the water to the tub/house and use a deep well socket,possibly a spark plug size and remove the whole thing..
then you can see the seat inside and if you can't "see" it you can use your finger tip to feel for cracks or gouges in the seat. if its bad it will either be an octagon in the center or a squareish,(is that a word)?hole for the "seat wrench to fit into, (available for min- cash) at Home Depot or the like..
But take the whoe thing out and head to the HIS, I would look for an ACE hardware type store for the "FOG" to help match it up or for last choice HD, Packing string comes in a small 1-2' roll and is nothing more than a waxy string covered in graphite, and the washers for the seat seal will be sold seprate too..,or you may be able to "match" up the whole stem.. should not be alot-$$ but could cost as much as $30 bucks new.. either way you have done the hard part already.. just remember that it should come in hot or cold, so check the "twist" of the handle and match it up.