Car trouble, can anyone help?

i drive a 2005 ford crown victoria police interceptor, i got an oil change and rear diff change a couple days ago, i parked it in the driveway only pulling it out of the driveway i noticed a puddle of fluid on the driveway where my car was parked, but the puddle of fluid came from the rear of my car, more specifically it looks like its coming from my drivers side rear tire, from the inside, i went underneath to check and it looks like its coming from the inside of my break disc and spreading onto my tire, thus onto the ground and creating a puddle of clear fluid, i want to say its my break fluid, but if anyone can give me more insight to this problem, it would be greatly appreciated thanks