Take the inside rear panel off and where you can get in give it a really good blast with WD40. You may also be able to give it a blast from the outside if you can get the nossle in behind the button.
__________________ VELVET BLUE UK INDIVIDUAL , IM THE LAST
UNITED WE STAND DIVIDED WE FALL
I stepped in a plate of Pasta the other day - now I have to worry about my Carbonara footprint!