Hi caer, try a little Goo Gone, that works here. If not try and wet the sticker, with a warm wash cloth and really get it wet. See it that helps to remove it.
WD-40 is a lubricant that is usually used with any thing that squeeks or needs to be lubricated to loosen something. Men use it a lot when working with their cars I think. You can usually find it in the auto section of a store.
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