Hi Conachair,
I have never liked rust - corrosion on my boat's ss, especially since when I attended a West Marine store rigging talk, by Brion Toss. Brion reccommended to everyone, to get a handheld 50 x microscope from Edmund Scientific, and look at your ss using that.
I did and was especially surprised, at getting a good look at the granular ss surfaces, and seeing surface pitting under the rust staining.
I read everything that I could get on the subject of rust on ss, but just recently someone suggested reading the ss guide on this website :
http://www.outokumpu.com/application..._113142858.pdf
What this ss guide does not tell you is that proper design of ss used in a salt water environment, needs to shed off not collect or puddle salt water.
Looks to me that there was not enough squeeze out of your assembly goop from inside the fitting, when it was screwed together.
What ever, you are certainly right to have concern about the rust, left alone, it will get worse and worse.
In your first photo, didn't I also notice a shade of rust between the lay of the dyform wire, too ?
Douglas