Hi Brian,
As you can probably see it is pressed in and with the key inside it does not depress. On the other side diametricaly opposite there is another round pin like this, also pressed in.
Regards
Dimitris
You could try drilling out the pin as underneath it will be a spring and at the other side of the spring a brass end cap/pawl, once the pin is drilled out the spring and brass cap/pawl should come out, only problem then is if you wish keep the same barrel and key once you've sorted out why it's sticking, is that you need something to replace the pin you have drilled out to keep the end cap/pawl and spring in place .
Brian
8227