[Benson]

If there is grease inside "bendix" it will stick and not engage.

The colder the temperature the worse it will be.

Clean with solvent and air dry.

use very light weight oil like "3 in one" oil if any...

Check to be sure shaft is not bent (most common problem).
remove starter and spin to see if it "wiggles"

Grease that has gotten hard or cold also effects "standard" Bendix starters.