FWIW, the best penetrating oil I've found is a product called "Kroil" from Kano laboratories. This stuff is amazing! But it is very thin oil & will seep into the tightest areas you could imagine (I guess that's why it works so well, duh! ; )) I don't really know how it would react to the boot, but I do believe that it is petroleum based, so be wary.
Paul
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