I've got a QS205 50H 3T and used the whole damn syringe. No problems with leaking or drag.
I read the directions, it said 5ml would do it but I figured the avg 500-1000w hub motor is much smaller in diameter and width. This motor weighs 2.5x as much as my last 1500w 600rpm ebay hub.
While the cover was off I slowly dragged the tip of the syringe around the mags basically letting them pull as much FF as it wanted while applying a tiny amount of pressure. Went around the circumference a few times until it was all gone.
I used some black silicone to reseal the cover after adding the FF.