The lock on my bathroom door won't turn to lock the door. I have used graphite and took it apart to apply graphite, but it still won't turn? The lock is from 1971 and hasn't been used in 25 years. Is there anything I can do, or should I buy new door knobs?

A new lock can be found online for $5 or less. HD and Lowe's carry basic locks for not much more.