They don't do an oil change at 5k miles. They do what's in the maintenance manual, which isn't an oil change. So I ensured a clean sump before the 10k oil change.
How many copper components exist in the brake system? A moisture test would be better, but even then the fluid could be stratified with the water down in the calipers. The brake fluid has looked clean in the reservoir, when the the stuff at the wheels was full of gunk when I've done flushes.