Again taking apart my acetylene regulator help

Hello again
After a couple of days the regulator malfunctioned again. This time I
really want to take my hand at repairing it, but again hit the wall. This
time I put pics of the regulator in the dropbox (acetyleneregulator*.jpeg)
What I cannot remove is the slotted thing (the valve stem?). I tried to
turn it in both counter and clockwise with a small tool fashioned with
some angle iron, so hard the iron bent yet it did not budge. Stopped
trying since I was mangling the brass. Perhaps one must push the valve pin
to pull at the same time the slotted cylinder?
I suppose I could take it to the shop again but I really want to learn how
to dissasemble it.
Any help thanked in advance
Mongke