yes it is corrosion since from the shop, now its worst, its an old stock. its been a year with me. i can consider different model with the following rule/criteria...
important criteria... footprint and dimension size (ie small), 1 turn only no need multiturn, you see the knob? thats small diameter and nice, i dont have to buy additional knob for it, just use as is directly. most important point is that its compact but yet comfortably controlled. i dont need high electrical spec since its only for mcu adc input (reading voltage level... hi impedance stuff), but the greater the resistance the better (> 1K ohm), to avoid unneccesarry current consumption to ground from the 3V supply. any mounting type will do, with condition it will not take too much space in the pcb/product. thanks.