Check with the previous owner as he will know if there was any oil ingress.
Other than that just make sure that the seals are soft and supple and that there is no deformation, wear or damage.
But you won't really know for sure until after they have been fitted I am afraid.
Also worth checking that the metal tubes are all good, these are cheap and easy to replace.
Pointless having good seals if the tubes are worn or out of round.