FWIW the last IBM 3505 I saw was in 1984. I remember one time the CE was called in to fix it (kept data checking or some such). Apparently, 3505's had optical sensors to detect the holes, and this particular unit was occasionally spitting machine oil onto the cards. As the machine oil soaked into the card you could hold it up to the light and see through it. The CE smugly announced that, from the 3505's point of view, the card "was transparent to the user"!
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