The oem fuel cap key wouldn't open the cap last night.
I drove the hinge pin out this morning and took pics of the inside for whoever is curious.
There are a couple of lock cylinder return springs that I took out and threw away as they were mangled. Just have to remember to rotate the key back to the center position when I close the cap. This is because the return spring for the latch is not strong enough to push back out once the key retracts it.
The reason for my key failure were the screws holding the latch together backed out. The cam on the cylinder to rotate the latch in was too far away from the latch cavity to pull in the latch.
You also don't need a key for an 81 kz440 fuel cap. There are no security pins or wafers. You could use a thin screwdriver or a pair of scissors.