A sign of failure of potensiometer

Yes.
If it's due to lack of use & dirt accumulation, then a small amount of suitable lubricating contact cleaner - or 3 in 1 oil - will usually restore them. "Deoxit Fader" is specifically made for use with pots that use conductive plastic elements.

If the failure is from wear due to use and age, or excess current, all you can do is replace it.

If the potentiometer has worn paths on the resistive compound and can be disassembled; bending the wiper contacts to sweep an unused 'track' can restore functionality. Done it several times successfully.
Passing a soft pencil eraser on the tracks can work too.