It it worn, or is it actual corrosion? They're pretty tough but after years of a person blowing into it the moisture may have finally formed a patina, like the green stuff on Lady Liberty. The only way to get rid of that is with a scouring pad. Even a worn connector will still transmit a signal unless a trace is cut. Unscrew the thing, see if something comes off by gentling using a scraping tool like a knife edge. If they're all shiny and coppery but just worn, then use a circuit tester (under $10, from most places you get auto parts, it's a metal probe with a light bulb, battery, and alligator clip) on each trace and see if any won't transmit. If they're worn down from someone previously using a scouring pad a little too overzealously, using a tighter connector like a Game Genie, a new 72-pin connector, etc. might help you get it to work.
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