I have a 2008 Saturn Aura XR. Recently my front right caliper was leaking so I replaced both front calipers and now I'm realizing that my rear left caliper was leaking also. Can I put my old used front left caliper(that wasn't leaking)for my rear left replacement?
For virtually every vehicle the answer is no. The reason being is, there is a front and rear bias as far as braking goes. The front end has (in every vehicle I've ever dealt with) larger diameter front rotors than the rear. Not only are the rears smaller, they are most likely going to be different shape and size.
In case you were wondering, here are images of the left rear then left front calipers. They are totally different.