Woodruff Key: 1 , Evan: 0

[Evan]

I thought the key had nothing to do with the socket / crank pulley other than alignment at assembly time - that the pressure from the crank bolt held the whole shbang together through static friction between the pieces

Yes, the woodruff key provides alignment for the sprocket/crank but without it the sprocket would never stay in alignment with the crank, and if the keyway is loose the key will eventually wear the keyway even further causing obvious problems.

What RJ said.
Ironically, worn keyways are a problem for 1990 and early 91 miatas due to a short nosed crank. So there is plenty of documentation on the problem of a worn keyway and workaround/fixes.

this is an example of what happens when a little play develops in the keyway, then the vibration of the pulley wears it away


of course mine is not that bad (yet?) but it could easily develop into that.
there is a loctite compound developed by loctite engineers specifically for this problem, its Loctite 660 compound. Ill be using that to fix this, or at least for a temporary band aid.
I wont be too happy if i put all this work in fixing the crank and the headgasket is shot / head warped from overheating....