One EQ knob feels very “gritty”

The low freq knob for channel 1 on my Prime 4 has developed a super gritty feel to it, not smooth at all like the rest of the knobs. It also seems to be getting worse, and I feel the knob will stop working or seize up at some point.

When I take off the plastic cap I see it’s held in by a hex nut — is this a user serviceable part? Has anyone experienced this before? Can I swap this with a proper working knob from a less used channel?