Gary’s right , don't use WD40, 50 or 60, it will never go away, most PCB or component cleaning spray on products are safe, manufactures have to adhere to strict codes anyway you are not going to empty the can on the wiper, if you do then you will need to get a technician to change the wiper, (potentiometer) 9 times out of ten Don is right it needs a clean.

Tony
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Tyros 4/Pair SR 350/ PC with a i8 intel chip, XENYX 802, Ford Focus 2 litre/Tascam DR07/Brother printer/Designjet 500/ our Doris/5 Grandchildren/ white boxers short Kymart shipped over and Typhoo Tea Earl Grey