Ah, I see where you're confused. Open and LSD are both called H233B, even though the guts are a little different. Same gears, same housing. Even the 33-spline rear end in the R50s (versus the 31-spline in WD21s) is still called an H233B.
The concept of the clutch-type LSDs in these is fairly simple. Imagine you've got a standard open diff. As soon as one wheel loses traction, the spider gears send all the power that way, and it peels out instead of pushing forwards. Unhelpful, right? Now stuff a bunch of clutches between those spider gears and the diff casing. The clutches make the spider gears harder to turn, and since spiders only turn when one wheel is going faster than the other, those clutches make it harder to do a one-wheel peel. The FSM says it should take at least 260 lb/ft to make the clutches slip. It's low enough that you don't chirp the tires on dry pavement (like you would with welded spiders or a spool), but high enough to give you a fighting chance off-road.
The clutches can wear down over time, but I can't imagine the kind of abuse it would take to get that 260+ lb/ft down to zero. Much more likely you're rolling on an open diff. As for the vent tube, unless the rear end is making horrible noises, I would just check the fluid and replace the tube... especially since you're planning to swap in an LSD axle anyway.