I removed the fitting on mine and was successful.....after two weeks! I tried every trick in my arsenal; penetrant, heat, tapping it, rocking it back and forth, etc. I cursed those narrow hex flats that they put on these fittings. I have no idea why they do that on such a large and difficult to get to fitting?
I remember the day that it came off. Having the wrench on it, the fitting moved and I just paused. Three things could have happened: 1) the wrench slipped off the flats 2) The fitting threads stripped the aluminum threads in the head 3) it actually let go and was coming loose.
Two of the three are bad, but luckily for me it was #3!