Used 5/8" close wrench to turn it counter clockwise, when loose used vice grip to pull it out slowly. I`m sure its rusted after you separate it into two piece you can use #320 or very fine sand paper to remove or clean both parts then spray it with w-40. If it goes back in smoothly, then used plumber grease to lubricate the o-ring then put it back. Luis

I had the same problem. I tapped the screw head a few times with a heavy hammer. This did the trick for me.

How do you put it back in? I can't get my 1423 to go far enough in to engage the threads on the brass cap. Leaving the stainless steel cylinder off, the brass head screws on fine, so I haven't buggered the threads.