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I have to say up front I haven't played with hitachi diffs a lot, but I've got some experience with diffs from ford/holden/valiant stuff. You absolutely can't re-use a crush tube. If you do, it'll tend to want to destroy the bearings. Ironically, or not, the same thing can happen even with a new crush tube, though in this case it won't be from overtightening, it'll more likely be from insufficient tensioning of the pinion nut. The forces on diff internals are massive, under power, the pinion literally tries to force the crownwheel away from it and spreads the housing. They are a tapered bearing, and just a fraction too little preload, and they'll allow a slight angularity and focus all the stress/load on one tiny section of the rollers, and fail. With the right clearance (in this case so tight that it's actually preload, or negative clearance) the load is spread across the entire tapered roller and it can handle very high loads in contrast.

If you can't get a new crush tube, the other option would be to get a _solid_ spacer made up so that it no longer crushed at all, and the pinion bearing preload was instead set by the thickness of the solid spacer. That is a pain to machine up (though you could use one main spacer, then a couple of shims a few thou thick to get you right on the money) but ultimately there's no guesswork or reliance on the crush tube to collapse just enough to get it right (which they generally do well, but anyhoo) With the use of a set thickness shim, you also don't have to worry about getting the pinion nut torque perfect, generally you get it as tight as you physically can (and you'll likely need to mount it in a vice or jig to hold it in place, and use a breaker bar with a metre long pipe slid over it to get enough leverage. Of course if you happen to be a weightlifter or something, that might have to be revised.