Happy New Year Garyk706,
I don’t think there is a “best method” to clean paper dials. Many people feel that doing anything beyond brushing with a very soft brush should be avoided. While others use chemicals like bleach, hydrogen peroxide as well as water to remove stains. I personally shy away from doing too much because of a few bad experiences I’ve had with them in the past. One thing that has worked ok for me is brushing back and forth with a fine brush and little corn starch sprinkled on the dial. I’ve heard that document cleaning pads that are used on old drawings, paintings and books work pretty well. I haven’t tried that yet but now that you’ve brought the subject up here and stirred my curiosity I’ll order one to see how it works.
I just did a google search for “document cleaning pads” and a bunch of resources popped up.