Behringer xenyx 1832 micer

Not in front of me yet, enquiring if known whether a batch of bad pots went into them, or maybe a serious case of Pbfitis. Only a year and a half old but for ages the owner has had to offset a standing , non varying, L/R imbalance using all the pan pots but there is also bad "scratching" of 5 of the channel sliders. Used in a personal studio environment so no abuses at all.