This device on a domestic knitting machine is often overlooked. We hear of cleaning the needles, cleaning the bottom of the carriage and other bits.
The brushes on the knitting arm also collect lint and dust. It seems to build under the brush wheels, more so than the rubber ones. These brush wheels can be replaced if the bristles are too worn. The picture is of a Silver-Reed/Singer/Studio chunky machine.
Lift off the lint and give the actual brush a careful look. You will more than likely see yarn strands caught up in the bristles. I use needlenose plyers to gently pull out the strands and not pull out the bristles. Of course, you can order new brushes if they are too distorted. They can be purchased from you Silver-Reed dealer and are very inexpensive. The rubber wheels tend to become brittle over time and perhaps should also be replaced while they are available.