They all look something like this:
See here: austin healey sprite transmission speedometer pinion gear
So, I ordered one on e-bay and it looked just like that one I already had :(
But I still was not 100% sure that it was broken. I wrote the seller and he sent me another one (I now have 3) and low and behold (I'm sure that's the correct idiom) the 3rd one looks just like I thought it should
So to correct for the internets lacking in the correct image to help with this repair: Austin Healey, Sprite, MG, Midget, Austin Motor Company, British Motor Company A-Series Morris, Speedometer Pinion Gear, Transmission, Stripped, Speedometer Cable:
Note: The one on the left is round (stripped) while the one on the right is square (fine).
Now, I just need to replace the actual speedometer :(