Q: Axle Damage 2005 Dodge Caravan

I was sitting in a parking space and forgot that it was a concrete space separator (I guess that's what the name of it is) in front of me and drove over the concrete parking space separator by accident and damage underneath the vehicle. I was told that my Axle was damage but I don't know if it was the front or rear on both sides damage. How am I able to tell if it's the front or rear in order to have the mechanic come fix it? Also, my vehicle some times smells like gas or oil and was told what I needed to have fix but forgot what it was called. The person told me to just make sure I keep my gas tank above half tank so the smell won't come until I'm able to have to gas tank or something fix. Can you tell me what it is that I need to have fix also on my gas tank?

Thank you for your help.

FS

My car has 220000 miles.
My car has an automatic transmission.