steell,
Yes. Everthing you say is correct. However, I have already checked al lthat out. Along with there being a starter clutch, there is what I call a 'slip gear' or 'ring gear' or 'oh shit gear'. It is a ring gear inside the starter (see part #12 on diagram you pasted). Two planetary gears normally rotate along this ring gear and turn the external shaft.
However, if, for some reason, the shaft is torqued quickly (such as a backfire) or stopped while under load (such as, ummm, if you jammed a screw driver through the sprocket), the 'ring gear' turns inside the starter (part 12) instead of messing up the armature or other parts of the starter.
This ring gear is held stationary by the pressure of the front and back of the starter as bolted together by the two long arse screws. If These screws are not tight enough, the starter will turn, but the slightest pressure of the external shaft will stop it and engage the ring gear which will spin freely. I have tightened the screws as much as I can, and it now turns the engine, but it seems to hit hard spots and instead of cranking up steady and it seems to hit a hard spot in each cycle. It still startedd after a few gut wrenching groans off a car battery, but...