Clean or replace contact strips

What is the success rate of cleaning rather than replacing the rubber contact strips.

The problem at hand is a Yamaha Clavinova CVP 605 that occasionally gives unwanted loud sound from a couple keys. Several years ago I cured a Roland KR5000 which had the same problem by replacing a couple strips.

BTW, I noticed a reference to conductive ink in another posting. Where is this available?

Gene