I've never need flux on any motor. I just make sure the wire and the tab's are clean. I've always broke in my S-600's and gotten good life out of them. Use the water method. Basiclly run the motor in a glass of water for 30 to 45 mins at slow speed. I normally just turn my throttle trim knob all the way up and let it run. I had well over 300 runs on an S-600 before the brushes wore out.