Actually, the problem appears to be completely unrelated to steering lock. I'm convinced there is some minor damage to, or defect in the actual ignition cylinder. Here's why I'm sure of this: Locking the steering wheel or turning it doesn't normally help clear the problem. I am familiar with this problem on this and other vehicles and the symptoms are different.
Curiously, what does work, everytime, is to apply gentle pressure to the key as if pushing it further into the ignition cylinder. When you do this the cylinder springs in and back out ever so slightly. Then the key works - every time.
It's still a mystery to me, but I'm glad that I have no troubles starting it for now.
Thanks all.
