IMHO, a starter is a go/ no go item.
It either works or it doesn't.   Hopefully you've done some basic
troubleshooting before you replaced the starter, to correctly determine
exactly what is wrong.  Am I correct in assuming that you have eliminated
the ignition switch, wiring and connections as possible sources of trouble?
  If (after proper troubleshooting) you bought any used part, and you bolted
it in, and it doesn't work, take it back out and return it.  It's junk. No
mystery there.
  It does sound like the solenoid internal contacts are burnt, and not
relaying 12V to the motor during engagement.
  As a side note; if removing and replacing a suspected bad part is how you
troubleshoot, that's your problem.  Parts replacement, as a method of
troubleshooting, is never the correct way of repairing anything.  It's
expensive at worst and lazy at best.  If you pay a mechanic to perform work
this way, you're throwing away good money.  A good mechanic is not just a
hired pair of skilled hands, he is, most importantly, an informed,
knowledgeable, thinking pair of brains.  When he ceases to think,
troubleshoot, consider other points of view, or just have an open mind in
general; he's dead in the water. He's wasting your time and money, while
assuring himself of job security and lining his pockets.

Mike B.

> There's a strong solenoid "click"  when installed, but no motor action. On
> the "bench" there's the standard  thrust engagement when 12v are applied
> to
> the solenoid, and the motor spins  when 12v are given to the lower
> terminal.
>
> Is this a bad solenoid not  giving juice to the motor? I can't figure it
> out.
> I'll be scrambling  tomorrow to find a new (or known working) starter
> regardless, so if anyone  know a well stocked resource in NYC I'd be much
> obliged. Still, its a  mystery.