I was off last week, and won't even apologize: The American idea of year-round productivity has its limits and creates its own pathologies.
Regarding the original questions:
1.These spring contacts are made of brass, and brass does not rust (it's an amalgam of copper and zinc) so rust is the wrong word.
2. I checked with three KK67 I have here, and they all have some level of tarnishing on some or all of the springs.
3. Most importantly: affecting functionality of this type of spring contact is never an issue, because, a. you are lookin at the underside of one of two contract springs, b. the actual contacts are heavily silver plated points that are self-cleaning
4. I addressed the question of how to clean tarnished plated XLR contacts here:
https://realgearonline.com/post/374346.
The same method applies to Neumann head contacts.
