Circle pad initially broke during a shell swap when my original lower shell's hinge cover started to crack. In haste to transfer the original circle pad, it was broken by my brother and then re-glued together in place with the new shell. This repair was temporary as I had the circle pad snap off with my thumb while catching fish in MH4U.
I immediately went looking for a replacement part, found this website and lamented not having found this information that day when I realized how easy it is to remove the circle pad from the device.
After looking at the guides on this site, I knew what I needed to do and set about doing it the day my replacement part arrived. It did look different from the original and I worried that would hinder its performance in the stead of the original circle pad. But after completing the repair I have noticed no hindrance at all.
With this repair, I got a little screw happy and started unscrewing the motherboard. I'll simply say, this is unnecessary, once you remove the back cover and expose the motherboard, you can freely access the circle pad and need simply to unscrew the control portion of the circle pad. Then just carefully release the ribbon connector and voila, there's the circle pad ready for you to replace it.