I have a problem with my Yamaha e373. I just bought this keyboard few months ago. Sounds fine, until all of my C# and G keys were all having trouble. These keys lose its touch sensitivity and sometimes doesn't sound especially if you are pressing it multiple times. The problem is also ocassional. Sometimes its fine, other times it's not. I've already cleaned my keyboard, and still the problem persist. Does anyone knows what might cause this problem to occur? And how to solve it permanently?