I've had to deal with a number of M923 family hubs already and not *one* of those nuts has ever been torqued properly. In fact, one of my non-CTIS trucks had an inner oil seal failure rear which looked like it happened because the hub nut wasn't torqued properly (i.e. not enough torque) which caused enough wobble/eccentricity to spread the seal.
The one I'm having a problem with on my CTIS truck in the front also looks suspiciously recently-serviced vs. the others and I bet I'll find incorrect torque values there too which likely sped up air seal failure. As to that plastic sleeve, I dissassembled a spare CTIS hub from a torch-cut rear axle just to see how it all went together and found out the plastic sleeve looked as though it had degenerated/ deteriorated -- almost as though some grease or oil contaminant had started eating it and making it brittle. Hope that's not the case in *all* of them -- as in some future plague-level CTIS disease.
The air is definitely puking out from inside the hub. You can feel a nice breeze all around the hub/ backing plate. I made an airline to throw 60-70 psi at the front CTIS system only and it's a pretty obvious failure.
According to the parts TM, there should be two different air seals on the rear: 1) 357974TA0/ 5330-01-272-1147; and 2) A-1205-D-2162/ 5330-01-308-0175
According to the parts TM, the front should just use two of the 357974TA0 seal instead -- but the maint TM says the above ^^^
Since I'm guessing the sleeve will have deteriorated too (and it doesn't look as though you can disassemble everything non-destructively anyway), the maint TM shows:
SLEEVE: 2245-H-1022 / 3120-01-271-8353
I've seen the various seals advertised, but never the plastic sleeve. Anyone know who stocks them?