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petecldJackpot!!!!! NICE find. Those cards look like they are in great shape. Plus you said some have "Yum-Yum" on them? Those are N403s and are worth MANY times what N172 are worth.
With all due respect to the people who have offered you suggestions for removing them, I'm sure their methods work but I say protect your investment and pay a professional conservator to do the work. It's more expensive than soaking them yourself but going by the image they are WELL worth the cost.