First of all, your connectors are probably made from brass, with some micro amounts of industrial gold plating on them. There is nothing to rust.
Secondly, alcohol doesn't catch fire? Were did you learn that?
Third, I would not leave the connector in there too long. I spent my career as a design draftsman and we use to use Usonic cleaners to clean out ink pen tips. If left in too long, metal is going to start to disappear.
I would rather have you spray your connectors with Deoxit-5 contact cleaner. It doesn't dissolve metal, and is a great cleaner.
Wayner