[BrianG]

Once you remove the screws, you can try gently twisting the heatsink as the thermal paste may have dried a little causing it to stick somewhat. Also, be careful with adding more heatsinks to the MGM. It looks like the current HS may be directly attached to the FETs which might put physical stress on the FETs if you add more weight.

That's kinda why I like the Quark a little more; the case is the heatsink and adding more doesn't physically stress the FETs.