On my Mark VIII the black winged piece on the exterior of the cylinder which turns with the key is loose or stripped allowing it to turn all the way around without a key present. Is this piece replacable ? Or does the whole ignition cylinder have to be replaced ? If so what are the parts I need and how can I go about doing it ?

Any insite would be appreciated..

Sounds like a lot of the cars my buddies stole.........I mean owned in the city :N . I think you have to buy the entire cylinder. You may be able to get it from someone around here parting a car out.