[eyi526]

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

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.
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.

 

[eyi526]

Civic has not had hydraulic power steering in a couple of generations, power steering has gone green all electric...

You're right. Great catch!