First, I would ask why you thought you needed to bleed them. IE did you change the axles out, or did you do something to disconnect the brake lines somewhere? Perhaps you were low and topped it off?
If you have not had to add any fluid then you likely have not done much in the way of trying to get a bubble out of the lines. Further, if you have brake fluid that is older than about (I think) 5+ years then you should consider flushing it out with new stuff anyhow.
I do not know about the calipers, if they would cause this or not. Personally I really want to go with the brake fluid first. When you are parked push on the brakes for a long time and see if you really do have a leak or not...(engine running) good luck to you.