Drivers side front caliper is not releasing

The drivers side front caliper is not releasing properly causing the rotor to heat up A LOT. Initially I thought the master cylinder was leaking as the pedal was slowly going down while holding the brake on. This was after bleeding the lines. I replaced the master cylinder and that problem was solved. At the same time I was smelling a nasty odor that I initially attributed to something dripping onto the manifold (which there was and before changing the master cylinder). Shortly after this I noticed the same smell and found the front left rotor heating up.I thought I had a failing caliper so I replaced it. 2 weeks later same thing. Faulty rebuild? Returned it, replaced it. 4 weeks later same thing starts again. Could a glazed rotor cause excess heat that causes the caliper to heat up and bind? ( Sliders are sufficiently greased) Could there be dirt in the brake line for that one wheel? (System bleeds with no problems)Could this just be a sucky after-market product? (Fits OK with no play BUT it IS a low end remanufacter)
Thanks
Steve