

It is either a type of rubberized material degrading or one piece of plastic in the group. Being a home-labber/gamer I have gone through a couple hundred mice easily. In addition to Logitech, I’ve had lots of stock MS/Dell/HP and even Sun mice. A few can get this condition with the materials. Often it will be a rubberized component, but sometimes it is a plastic part. Like the mouse wheel is a more common part that gets sticky, but the rest of the mouse is okay. Nothing happened other than it sat around for a long time. It could be that the last user had grubby fingers stained orange from cheetos whilst using that mouse and that lent somehow to the degradation. Hard to say. Plastic does degrade for sure and maybe our grubby mitts help?
They won’t. AP sanewashes everything.