If you cleaned them and the rust still did not come off, the gold plating probably wore down to the base metal. It probably also means they were either used in an application where they were repeatedly plugged in and out, and you should see the wear lines on the connectors themselves, and/or they were plated after 2002 when industry responded to the jump in gold prices, and tried different methods to plate gold more efficiently. If they were off batteries, it might be rust deposited rather than worn down to the base metal.
Sometimes, and I have only seen this twice, the environment and applications conditions as well as usage, conspire to actually bubble or start to deplate gold, then the metal underneath the plating starts to rust. If this is the case be careful your ultrasonic cleaner doesn't agitate it off.
By the way, brilliant using your ultrasonic cleaner, when refiners find a good clean source for pins and connectors, like a good meal, they want seconds.
Scott
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