Remember what was said about "field coils" in the genny? That is what is wrong with your old gen. The permanent magnets the field coils are wound onto are what makes the low voltage needed to get a signal to the regulator. Current from the regulator to those field coils increases the magnetic field strength and increases the gennys' out put. If the field coils are bad, no change in field strength and no more current out of the genny. Genny will motor with bad field coils. It won't motor with a bad armature or bad brushes, or a bad commutator. Field coils are hard to test. Little resistance in a coil of wire. So for future ref check the volts at the field connection. You should see the working volts need to boost the out put. If the field coil is shorted, common. The volts will be low.
