Looking for a Dewalt D55146 regulator part

[deomo]

I have a D55146 type 4 that is leaking air.  I bought and installed the regulator pair kit.  However, after putting the parts back together onto the manifold, I can't seem to rotate the pressure adjustment knob (1) as shown in the attached image.  The parts inside that pressure adjustment knob 1 are parts 2, 3, 4 and 5.  More specifically, part 4 seems like it should rotate as part 1 rotates but it does not.  How do these parts work together, and is it possible to buy part 4 online?  Thanks.