The quality of your pot is important. Many now use very thin metallized plastic film rather than cermet, so they film metalization flakes off and gets pitted if there is any current surge, making the adjustment very intermittent and exasserbated when the cap discharges and then the contact has to charge up the cap. .. which is why a small cap and bigger R filter is better for wiper reliability. THese film trimmers and pots are rated for very low power and can easily melt when near the extreme setting with a large cap load.