a pipe wrench can fit onto any part of that fitting and as it turns it grows tighter on the grip. Squirt some anti-seize around it and if all fails grab the vise grips and lock onto it. Might take the brake hose off intake and go in at an angle from the side to catch a flat spot on that fitting. Vise grip on any portion of the fitting will grip but be careful not to crush it. Put something in the hole to keep it from distorting the thing or crushing it.