I'm not a locksmith, but I'd disagree with him on two counts. Graphite is made for locks and it was not what was causing your problem. Could have been that somebody sprayed WD 40 or something similar into and it rusted up or it could have been from not be used in a long time. The door locks in my Vette didn't work when I got it and that's what I used to free them up and they work fine. The old style lock mechanisms are fairly easy to deal with, I've re-keyed many, Ford, Chevy and Dodge.