Known as a trackpoint or laptop nipple, these bits of rubber are remarkably simple to get replaced and can make a world of difference if you use this centre stick a lot. Just a small amount of dust can make it move when you are not touching it and if its worn out, its even worse. Below is a guid on how to get it replaced.
You’ll need to get yourself a replacement rubber and a pair of tweezers or long nosed pliers. As with any hardware work carried out on a machine, shut down your laptop and remove from all power sources.