I've never used anything but compressed air on my synths. I've always felt that any type of liquid would eventually produce an unwanted residue. I do, however, use electronic cleaners on non-moving parts such as circuit boards, etc. It also helps to use a dust cover. A towel or anything will do. Don't buy one. If it must look nice, if you or your wife sews, you can custom make one for about a bucks worth of material.
chas
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"Faith means not wanting to know what is true." [Nietzsche]