"Bendix" is not really the correct term!
This was made in the old days by the Bendix Company.
This had a small gear running on the starter motor output shaft.
When the Starter Motor was energized this small gear would shoot up the shaft as there was a spiral track on the shaft.
So centrifugal force would fling the small gear out in one direction, it would engage the flywheel and turn the motor over.
Releasing the starter key would cause the small gear to fall back out of the way.
The newer systems such as our Jeeps use do not have this small gear flying up a spiral track but has a Solenoid flip it out to engage the flywheel. At the same time inside the Solenoid assembly two large flat copper contacts are bridged together.
This then supplies major current to the starter windings to turn the engine over. When the key is released the small gear drops down again out of the way.
So for our Jeeps there is a very thick red lead going direct from the battery positive...unfused....to one of the flat copper contacts. When the solenoid is energized it connects the motor to +12 volts.
So the point here is that the solenoid needs to be removed from the Starter motor and the copper contacts inside it that carry all this current need to be cleaned nicely...even filed down carefully to obtain a good contact when the solenoid bridges the outer flat pieces.
So the whole Starter Motor may not need replacing but only the Solenoid needs a good service or replacing. The motor itself though could have a bad commutator or brushes or the solenoid gear could be worn.
The starter motor has a large lug on it that the thick red cable connects to....is always live...make sure you disconnect the battery completely before removing the Starter Motor assembly!
There is a Starter Motor Relay in the fuse box under the hood that operates the solenoid via a smaller lug on the Starter Motor assembly. A bad Starter Motor Relay contact could cause bad solenoid switching ability...easy to swap that Relay over!
Check all lugs on the motor assembly are on tight.
If you replace the starter motor complete with the solenoid attached it should fix your problem but some work on the solenoid only may do the trick.
Missing teeth on the flywheel should also be checked for as suggested!