You'll be best off to get an overhaul kit, synchros, bearings, thrust washers, seals and so forth. While the seller may have told the truth about shifting smoothly, it's what he didn't say that may be at issue. If the shaft bearings are marginal she'll howl at the moon and sun. If the synchros are worn it'll likely jump out of gear on deceleration. So while you've got it out of the car you might as well freshen it up and prevent future grief.