I have used 99% Iso to clean my cobs a couple times now. I just did a thorough shank/stem cleaning on all 3 with pipe cleaners and swabs wet with Iso. They came out very clean, but they "fog" the interior of the amber stems and actually begin to dissolve the outside of the stem if you get it wet with alcohol. I noticed this as I was holding the wet stem and my finger print was left in it. You can polish much of it out if you want to be bothered (it's just a cob). But it does seem too harsh for the stock stems. I found that if I hold the stem upside down and carefully clean the inside of the black stems you could keep it from getting on all but the tip of the button and avoid any noticeable damage. But I just thought I would post this so others would know before they do the same thing I did with 99%. I may either just use a milder liquor in the future or at least dilute my iso a bit first. I like 99% though because it is strong and works well to dissolve nasties.
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Rookie, but learning.