Mouse button playing up

The left button on my mouse suddenly decided to stop working properly. It registers a click after you press it a few times, or if you press it really hard, and the click will drop-out in the middle of a drag, Really annoying.

I’ve tried opening it, but with no luck. I doubt I’d be able to fix anything, anyway.

Does anyone have any idea about this? it’s a Logitech Wireless Optical Mouse for Notebooks.