Radiator internal failure causing engine coolant and transmission fluid to mix causing transmission to fail.
I took my xterra in because it constantly blew hot air. upon inspection i was informed of the tsb issued by nissan that the radiator tubes can crack and mix coolant with transmission fluid and that i was low on coolant because of that. the tech informed me that the leak was minimal but needed to be replaces asap. the radiator was replaced and lines flushed and also had to take my car into a trans expert to flush and inspect the transmission