Pure American brilliance thank you.
We hope your Nation is able to heal after the recent events there and one day we want to visit again and see more of the beautiful countryside, although it will be a long time for us to save enough I reckon.
We have a basic home theatre here at our 'Sheep Station' (ranch) in Western NSW and have used Sony RM-VLZ620 RCU's for about fifteen years, so to be able to repair them as comprehensively is brilliant.
Over the years I have used ISO Alcohol on the PCB and mild detergent on the mask but, as you describe, the conductive contact is eventually worn out.
It is magic to have our oldest unit so sensitive again, yet not too sensitive, original, exactly as all other buttons' on the mask.
No overlaps on the first try !