modern truck question

The stepson traded off is Dodge Ram with the eco diesel a few years ago becasue the dealership never old find the occasional colliant leak, and got a 2019 or 20 Nissan 3/4 ton with the Cummins. AC goes out other day with about 120,000 mi. Takes it to the Nissan dealer and they find a leak in the "tank" and a bad EGR. $300 labor plus $2700 parts. Exactly what is the "tank' on this Nissan marvel??? $2700 for parts?????