[James]

I just sent pictures to Glenn, which collectively illustrate the parts shown by Don as a working assembly. After inserting the key, I push inward on the assembly while turning to release the tension on mechanism so that the tabs will retract. Essentially, the locking mechanism is under some tension, and this needs to be "countered" by pushing it inward to get the lock to release. Of course, lots of penetrating oil is helpful if the mechanism is oxidized.