Kappa top box repair

[ted_paper]

Hi,
Not sure if this is the right place to post, but I have inherited a Kappa top box but unfortunately the press release button is sticking and will not return.
I thought it would be an easy job to remove the lock and investigate but can find no way to remove it. There is a small retaining screw in the box which I have removed and allows the lock to wobble slightly but not detach. It looks as though it should slide down and out, but it fouls the release button...
Any suggestions would be welcome as this is driving me mad!
Couple of photos attached to try and describe problem a bit better.
Thanks

[sye]

Have you tied gently prying the release button upwards, it may just be clipped around the edges?

[ted_paper]

Yes, that's the only way I can get the button back in. When I press it in again, it sticks!!