SPL SMC potentiometer "slack"?

I bought a used SPL SMC monitor controller and the volume pot has some slack, or free play, before you begin affecting volume. It's like the steering wheel of an old Jeep Willys, you know what I mean? (english is not my first language). You can feel when it starts moving the contacts inside, as it takes more force to turn it. Once it is turning the contacts, you turn the other way and it travels some 5% pretty easily and light before it catches the contsct again and gets a good resistance again.

Apart from that the knob works perfectly, with no noise or channel imbalances and the shaft is pretty snug in the pot, not loose or anything.

Have you ever seen this behavior before? I never encountered any knobs like this.
What Can I do to fix this, apart from replacing the knob?

thanks!