1996 Dodge Dakota Charging System Start Truck Engine Runs Fine After

charging system problem. not charging ,when i start the truck the engine runs fine after a minute or 2 the maint.requird lite comes on. i took the truck to auto zone and they tested the charging system. they said the voltage regulator was bad. i think the alt.may have worn brushes. should i replace the brushes or replace the alternator? i think it is a nippendenso alt. truck has 318 V8 Magnum engine
John