BB's on older bikes are a service item that is often neglected. Anytime you pick up a older bike i would be well advised to service the BB and wheel bearings. The grease will dry up with age and you will destroy the bearing cups and cones if that happens.

80's bike it probably has a square taper shaft. A Shimano UN54 sealed unit will probably plug and play. Need to measure the width of the old spindle. Looking about $30 for the part and what ever labor the shop gets you for. Its a 20 minute job as long as nothing is stuck.