I was lucky to get a metal DIRAVI splitter box on a trip to the UK in 2004.  The 4-speed box had two speed-related outputs, one at the differential, the other at the end of the main shaft, by the left wheel well.   Citroen made a 5-speed from the 4-speed by adding another gear to the end of the 4-speed box.  But, this extra gear made the box longer, thereby displacing the cable connection for the speedometer.    So, Citroen made a little gearbox that provided two speed-proportionate outputs, one for the speedometer, the other for the DIRAVI steering assistance regulator.
View of splitter with labels:

Gallery of other sides of splitter:
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Separating the splitter
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Top half of splitter.  The long shaft extends down to the differential.  Note the indentations at the upper right and lower left corners.  That way, the splitter cannot be reassembled incorrectly.

Lower half of splitter.  The hexagonal opening is for the long shaft to the differential, visible in the background. I took these pictures as I was cleaning the old grease out. 
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The small shaft and gear

Upper Section after cleaning.  I originally packed it with synthetic grease, which turned out to be too heavy.

Lower section after cleaning.  The long shaft is on the right side.  The center spindle is fixed to the case.   Note the protruberances at the upper left and lower right corners, to ensure a proper match of the halves.

Lower half with the shafts and gears in place.  The shafts turn at a 1:1 ratio.  I checked.
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The disassembled components.    Very important to keep these parts clean, so I did the work over unrolled paper towels.
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As I mentioned,  I originally packed it with synthetic grease, which turned out to be too heavy.  I refilled it with gear oil.  I'll have to keep an eye on it, to be sure the oil does not leak out.  I stood the splitter on clean paper towels for a week, and no leakage.  But this does not mean that it will not leak while it is in use.