If the key is worn, chances are the tumblers are as well. Don't know anyone in Langhorne, PA but I highly recommend Leon Rowell in Montezuma, Iowa. leon429@zumatel.net or 641-623-1957. Reasonable and fast turn around. He can fix anything that ails it.
Sometimes the tumblers can get sticky. I've had success before by spraying degreaser and silicone spray inside the barrel with the tiny straw that some cans come with. Remember plenty of rags to prevent the silicone and dirt staining your floor when it drains out. Turn your key plenty of times to dislodge any particles and coat the tumblers. Let us know if this helps.
Thanks for the info. I have been spraying oil in the key slot. I'm hoping I don't have to remove the lock cylinder. This car has been sitting since '74 and I don't know how long before that. ( I been working on it for the past 6 yrs.) 65k miles original miles, I hope the tumblers are O.K.