Hi Michael,
Thanks for the link.
Ours also operates a rod that controls a catch at the top of the door and one at the bottom.
Had a look at our lock itself and it appears to be sealed and dosent lend itself to be stripped and repaired.
------------- I started out with nothing and I've still got most of it left - Seasick Steve 2008
I had the same problem a while ago! The button was screwed on too tight. I slackened it off and it started to work OK for quite a while, then it tightened up again....it would appear that it can do this in use.
A while later I took it off and set it on with a little superglue, to stop the button from turning in use and I have had no more trouble from it
Of course yours might be worn internally, but it might be worth a go at this too.