Yep...
I made one from a 30MM Chrome-Moly Alloy-Steel 1/2" drive Six point Socket...
Used a 4" disk grinder to cut the reliefs for the 4 teeth....
The teeth are about 7.5mm wide and about 8mm tall....

I am still a bit mystified about this failure....are you saying that the flex disk and Tri-flange yoke the flex disk is bolted to (is not) turning....

But the output shaft the Tri-flange is bolted to with this special 4 slot nut (is) turning when you turn the input shaft on the clutch side of the trans...?

How can you see the output shaft if the flange is still attached to it...?
The oil seal of the output housing on the trans rides on the flange that is splined to the (buried) output shaft....not trying to be too picky and detailed here but am still confused with what you are seeing....

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1978 Yellow 300D (The Mustard Toad)
1980 Blue 240D (The Iron Toad)
1989 Grey Mitsu.4WD Mighty Max Pickup (Needs a Diesel transplant bad)

(Open the pod bay doors HAL)