This does not apply to the 2K+ and many other newer vehicles. You are referring to vehicles where the key, while in the off position, will also lock the steering wheel from turning. In many new vehicles, the 2K+ Bonneville included, the steering wheel doesn't lock. Our ignition switches are mounted in the dash and don't function the same way.

I would not be too concerned about WD-40 and sources of ignition (in this case). Unlike many older vehicles where there is the potential for more current and spark generation in the ignition switch, this is not the case with the 2K+ Bonneville. Virtually everything related to the ignition switch in these cars relates to controlling the input on a module at extremely low current. There is virtually no chance of spark or ignition with the few milliamps passing through the switch contacts as it grounds the appropriate input on the body control module. All the high current switching where a spark may be generated is isolated elsewhere in the vehicle.[/QUOTE]

This same problem occurred in my 2002 SE and it required replacing the key cylinder. You can try the method with WD-40, but I really suspect it won't help a lot. You're likely looking at some replacement parts.

Powdered graphite is actually a better lubricant for locks. Liquids, depending on whether they completely evaporate can leave a flim that will collect dirt and dust contributing to further problems later. This is frequently use by locksmiths.

My wife'* 2001 Bonneville is enraging her by not allowing the ignition key to be turned at all. It'* done it to me a couple of times; I just remove the key, re-insert it, and try again. So far that'* worked for me, but not for her. She tells me that she has to open the drivers door, leave it open, and then the key will turn and the car will start. I have used graphite lock lubricant but she still can have the problem. I had a new key cut at the dealer two days ago ($42...ouch) and so far there has been no problem, but this problem can be very intermittent.
I'm leaning towards the ignition lock being worn if the new key doesn't solve the problem, but she is adamant about the door being opened to get the lock to work. Since she drives the car far more than I do (it'* her car), I'm looking into the possibility that there is some kind of interlock that affects the key from being turned. I've noticed that the key cannot be removed if the shift lever isn't in Park--you just can't turn the key back to the full off position. I'd like to know how this feature works because I wonder if this can become a problem for turning the key when starting.
Right now we have a "wait and see" attitude due to the new key, but I have a strong feeling that the problem is still there and I better be trying to figure it out.

The problem is more then likely a worn key or worn cylinder.