if the pulley pops out more than the thickness of a finger nail then you found the problem

This page seems to agree with your suggestions:

http://www.miata.net/solo/99miatathrustbearingfailure.html

I'll take a look when I get home.

That page keeps repeating one thing, "change your oil regularly and religiously". Ooops...

...to say that the servicing and hence oil changes have been erratic over the last couple of years would be a major understatement.
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