2-gun,
From the sounds of it I'd say 2 things are possible.
Chemical reaction from the lubes and cleaner or between the lubes,
Or flatly, plain old failure of the Lubes to preserve.
Have run some short term tests on a weather plate and have found plain old Valvoline 10-30 is better as a preservative than Militec, as is Hoppe's gun oil, and I'm suspecting Crisco might be better as well.
Seriously, the Militec might be a lube(Pressure ratings I have seen have shown the stuff to be slick but not so good on hig pressure points) but it is NOT a preservative in any manner.
Tetra is solid stuff as a lube preservative, it ain't the best, but is a darn sight better than about 80% of the stuff on the market.
This leads me to thinking that possibly the chem reaction between two or three of the cleaners/lubes used might be at hand.
Get the rust outta there, and try it again with nothing but the Tetra after you neutralize any cleaning residue with the Rusty duck or Isopropyl alcohol.
I hate rust!!!!
And you ain't alone in noticing Stainless steel will in fact rust.
The Neighbor dog decided to "Mark" my new All stainless BBQ grill the other day and it's rusting where the Cur Peed on it.
There's a load of rubber buckshot in the backdoor gun with the Mutt's name on it!!!
Also have had a stainless colt rust a bit on the MIM parts after a day or two camping/Backpacking without cleaning while using Breakfree as a CLP.
Best lube preservative I have found is TW25B from Mil-Comm.
It was made for the Navy originally, for use on Deck guns and has a 500 hour continious salt water spray rating.
Whatever ya use, look into the incompatibility issue you may have found.
Best of luck!
S-28