slant six ignition issues..shuts off wont crank

have a 74 duster here, no mods at all, clean 52000 mile car. the ignition cylinder seems a little sticky, but when she cranks she fires right up and idles great. twice driving around today it suddenly shut off and when i turn the key theres nothing, on min later (about when i push the car to the side of the road) she will turn over and run. what is this????????? thank you-travis