Air Venturi (G4) - Hatsan Pump fix

[BigTinBoat]

My pump is not sealing and is giving the same symptoms as a bad "Final" o-ring, but it is good.
This pump is different as it has a "collar" that the o-ring fits on. The collar drops down when rod is pulled up to allow air in and then it is forced up when rod is pushed down. Now I'm figuring that there must be a "seal" of some sort between the rod end and the collar, but it's too small an area to see into. I thought maybe o-ring but I can't get it out. (Tried a micro screw driver but even it doesn't fit. With a 10x loupe I can faintly see what looks like a black substance, but can't tell what it is. From the way the collar spins on the shaft my thoughts ar ethat there must be some type of sealing surface there or it would not seal, right?

Any body take one of these apart?
Anybody know if the brass end is removable from the rod? Don't want to force it and break the end.
I will be attempting to call Air Venturi during business hrs when I get a chance.