Just reading between the lines and I hope I'm wrong, if the bleed nipple is showing any form of brake fluid leak then it's threads will have already have been lubricated by same. Dedicated release fluid may help but not as much as on a dry fixing. I do wonder if this particular nipple has been overtightened in an attempt to stop the weep?
It's a dilemma but the hollow construction of bleed and grease nipples means that with almost any correct size ring spanner the nipple will shear (and suddenly) before the flats give way, given too much force!
