Very good guide! The replacement scroll wheel I got on eBay did not have the black plastic part that sits on top, so I had to remove it from the original one. I did that by pulling the clear plastic part away slightly and removing it (do one side first and then the other side).

I able to access the scroll wheel without removing the cable. If you do that, I recommend placing some sort of object against the top half of the mouse so that it doesn't move and pull on the cable. I have fairly small hands though so you might need to unplug the cable.