Bill,
Thank you for the pics. From what I can see, I'm doing everything correctly, which makes it even more frustrating.

As you allude to, I really don't think I need the pliers to force the black ring to turn. I can wiggle the ring. I'm sure it's the tab doing it's job in not allowing me to turn it.

I suspect that for whatever reason, the tab is just not being pushed down despite the force I am applying. I soaked the lock with lubricant, hoping that would help. I may mess around with it again tomorrow.

If the key does bind up again (as I said earlier, it has only happened once) I will start calling locksmiths and mechanics to see what my options are.