Astro Ignition Cylinder won't turn

In order to start my van I have to sit and jerk the steering wheel back and forth while twisting the key. After a while the key will finally turn and the steering column unlocks, allowing the van to start. Sometimes it starts after about a minute of playing with it, I have also had to sit and play with it for over half an hour on occassion.

Should I be replacing the ignition cylinder or the steering column, or is there a way to just grind away the steering column interlock? Is it just a matter of an old key, and I should have a new one cut from the key code?

I haven't taken the mechanism apart yet to see how all the interactions work together.

Its a 1996 Astro; base model with 275,000 km on it - still running strong, but a little rusty. I don't know the engine size off hand.