I don't mean to be disrespectful, but..
If the system is full of brake fluid, and all the air bubbles are bled out of it, then I believe the only way to get moisture into the system is if the brake fluid absorbs it and carries it around the system?? So if DOT 5 doesn't absorb moisture, then the system should be safe from moisture-based corrosion internally.
I think...
...please enlighten me if I am wrong!
-Sam