Search for Caig Deoxit Fader Lubricant, it's available in a spray in different sizes or needle dropper from many sources.
These products can help perhaps only temporary. It may be time to replace the pot but since it's only the HP level control it's not critical like the input level pots.
Here's another thought, the solder connection on the pot to the circuit board may need to be touched up. Worth looking at if Fader Lubricant does not seem to help.