Yeah - standard pots used in most arcade monitors are not intended for constant use - maybe as little as 100 turns for the cheaper ones. The carbon film layer is fragile and can get worn pretty fast. Hopefully resoldering the joins will help, but if the carbon film layer is worn then not much you can do except replace it.
For this reason, I've been using cermet (ceramic-metal) trimpots for my projects lately, where possible, as they are rated to last around 50k turns, about 500 times longer than carbon film pots! Adjustments are smoother, and there are both single-turn and multi-turn (even finer adjustment) varieties. Cermet trimpots cost a little more but are not hugely expensive. Bourns is a popular brand. You'd just need to find the matching ohms rating, footprint and orientation.