When you say this, I am assuming that you mean by hand?cseger1 wrote: back together and it spins fine.
After having a starter apart, I always test it on the ground, using a set of jumper cables and a remote starter switch (or garbage screwdriver, same thing ). No use reinstalling a dead starter.
My hunch is that you may have a shorted commutator--the cheaper rebuilders will only clean up used commutators--well, they're supposed to test them too, but . . . they can fail--the insulation can give out, and it can slowly happen over time. Can have a short in the field windings also, and this will consume major battery current when the solenoid is engaged.
Other than that, the problem may be in the solenoid, which is what you probably hear clicking. Once the solenoid engages the drive gear, it's supposed to close a set of high-current contacts and start the motor a spinnin'. To check this, have the starter engaged and check for voltage (use meter or test light) at the terminal on the solenoid that connects to the starter motor itself--if close to battery voltage is present, then solenoid is probably OK and it points to commutator or field winding failure. If no voltage, then high-current contacts inside solenoid are probably to blame.
BUT I can't tell you how many times I've been burned by bad battery terminal connections, where a low current (enough to run headlights) will pass OK but when you go to start, no dice. You've probably been all over this already, but just in case, double-check things again.
I think most of us here have been where you are, at least once. Hang in there, you'll get it figured out. I have learned to quit working on my rig for awhile when I get really mad at it, else I start banging on delicate parts with a heavy object!