If the button test profile confirms that there is a hardware issue but your mouse is still within its warranty period. Then please
with your purchase details to resolve the issue under warranty.
The main body of the Z is held together with 7 screws in its base. 5
of these are easily visible once you remove the magnetic feet from your
mouse, but two are hidden under the label at the nose of the mouse. So
you will need to peel this off to access them.
The locations of all 7 screws and highlighted in the image below.
Once the 7 screws have been removed the top and bottom halves of the
case can be separated. However you need to be careful when doing this as
there is a small circuit board for the thumb buttons which sticks up
from the bottom half of the case into the top. Also, there is a thin
ribbon cable at the rear of the mouse which connects the two halves.
So when you are separating the two halves, do so gently, and with a
direct vertical movement. Keeping the halves relatively parallel until
you clear the thumb button circuit board.
Don't worry if the thumb button PCB pops out while you are opening the
case. It is connected by another ribbon cable and can easily be placed
back into its slot on the base.
The thumb button PCB, and ribbon cable are highlighted below.
Once the top half has cleared the thumb button PCB, the ribbon cable
is long enough for it to be placed down on the table next to the bottom
half.
Next you'll want to detach the ribbon cable connecting the two halves of the case. There are two black latches where the ribbon connects to the PCB, pull these out a few millimeters and the ribbon will slide out without any resistance.
With the ribbon detached you can put the bottom half of the mouse somewhere safe out of the way. Next you'll need to remove the main buttons and triggers, this requires removing the four screws highlighted below.

With those removed the buttons need to be pulled out of the top half of the case. If the trigger button caps are still attached I'd recommend removing them, as that can make this step a bit easier.
The buttons can be removed one side at a time, but you will need to get the main button, trigger, and fingertip assembly for each side all at once. So start by lifting all three plastics pieces slightly off the posts where the screws held them in place (highlighted in Orange below).
Once they have cleared the post, start pushing them towards the red circles. At these points the buttons hook onto the case, so you want to unhook them by sliding the buttons forward.
Here's what those hooks look like with one set of buttons unhooked, and the other set removed.
Once unhooked, the three buttons can be pulled out of the front of the mouse. Try to keep all three stacked tightly together, as if they start to separate it will be more difficult to fit them through the gap.
After removing one set of buttons you will be able to see the "trigger pull" switch for that side of the mouse. If you're just going to apply some contact cleaner to it this could be done without dismantling the mouse further. But if you need to remove the PCB completely to replace a switch, then you will need to repeat the last few steps for the buttons on the other side of the mouse.
With both sets of buttons removed you will finally have full access to the PCB. If you need to take it out of the mouse all that's left to do is disconnect the force feedback motors plug. It can then just be slid up and out of the case.
Reassembly should be relatively straight forward, getting the buttons back in is the most awkward part. But if you just make sure that you keep the three parts together, and get them over the hooks at the front of the mouse before trying to push them down onto the posts at the rear it should go smoothly.