Logitech mouse middle button not working

[silverwolf0]

The cordless mouse that comes with the Logitech s520 combo has dveloped (working fine before) a wonky middle button, and I can't tell if it is software or hardware caused. Pushing the middle button/scrollwheel usually displays the autoscroll icon in IE or firefox, but nothing happens. My scroll wheel works fine however. I've tried replacing batteries, installing logitech setpoint, uninstalling then reinstalling from device manager, putting it next to the receiver, nothing seems to work. If I turn off the mouse and then turn it back on, the middle button will work briefly, then gradually start dying as it requires longer pushes to activiate autoscroll until eventually it stops working again.