This. The owner's manual should be your first resource. Oil, Transmission, brakes, coolant and power steering is probably all the fluids in the car.Your car with the current mileage, if you have not changed the transmission fluid, brake fluid, coolant.
Do that ASAP.
On my own 2012 EX 5Spd/Auto:
Transmission every 25 to 30K miles
Coolant every 2 to 3 years
Brake fluid every 2 years
Below is from the owner's manual... follow it and you will be fine.
View attachment 496461
Also can be helpful to know where you are located, city/state
Also, the Civic doesn't have a rear differential and I'm pretty sure there's no transfer case, so not sure who told you that.