Taipan Vet I rebuild please help

[Bngen3]

Hi All,
Replacing all O rings and testing reg to find leak. I found a shredded one at the pressure gauge, broken valve seal. but I'm now stuck on reassembly at the fill probe. It seems I can't fully tighten it because if I do I can't put the cover back on and fill probe will not fit.
Any ideas why ?

 

[Bngen3]

Ok I got it sorted with help from @Vetmx. I was over thinking it that it had to be tight to tube but it doesn't

 

[rangur1]

Correct on the fill port piece. the valve seal poppet is carried by talon tunes.

 

[Motorhead]

Threading of the Filler assembly DOES NOT bottom out, it is designed t be backed off some so rotation allows gauge face centering or probe placement alignment.
As shown it is threaded in too far, ideal position is having probe hole close to front to back centered within the rotating cover sleeve.