I have a local rebuilder and keep a couple of spares for my vintage cars. My rebuilder said that as long as the seal has never been exposed to coolant, its shelf life is indefinite. The bearing is packed with grease, so no problem there.

Just store it in a dry place. I usually also put the parts in ziplock bags and press out all the air on the dry Santa Ana wind days we get down here by the beach in the fall.

Duke