The potentiometers can be opened but they are not designed to be...and there really is no point to open them.
They can be simply flushed clean with either WD40 or a switch cleaner, you will be able to see the wiper and board (pictured above) fairly clearly through a gap in the outer pot cover.
As said, eventually the track on the board wears out but so far (for me), a simple blast with the WD40 fixes it untill the next time.