I might be a little late to the party here, but on the '72 CB500 I was working on whose boots were literally hard as a rock I used 1 part wintergreen oil to three parts isopropyl alcohol in a big canning jar with a lid (4 oz wintergreen to 12 oz isopropyl alcohol) and let them sit for about a week, maybe two...and they came out like new! Soft, supple, the whole works. I really couldn't believe it, that treatment actually works! And they smell nice too! I didn't really believe it when I read about it, but what the heck, I tried it - and it does work!