I came across this post while having the same double-click issue with my copperhead. I've found that the cause is the plastic contact under the left click button itself. It wears out and takes on the shape of the microswitch underneath. To fix it all you have to do is follow the instruction for taking the mouse apart posted above and lightly filing the plastic contact flat again. You only want to take the notch out of it.

How to open the mouse (will probably void warranty):

* you need: a crosstip screwdriver, a pointy tool (like a small screwdriver), pincers

- unplug the mouse!
- remove the rear foot of the mouse using the pointy tool and pincers. Do not damage the foot nor touch the sticky side!
- remove the "QA" sticker from the hole where the foot was before, use the pincers for that
- remove the screw in the hole
- lift the rear end of the lid of the mouse about half a centimeter
- pull the lid back to unhook its front

You should now have access to all relevant parts. Avoid touching electric contacts when possible.

To close the mouse:
carefully place the fiber optics back in their groove, hook the lid in at the front, push the lid forward, close the mouse, put the screw back in, put the "QA" sticker back in, place the foot back.

I don't know about the click problem or the glueing of bumpers, I only had to fix my mouse-wheel.

Soem physical abuse solved this issue for me. I banged my copperhead with the plam of my hand. Haven't had the problem since.