Thanks for the post.
The problem is only on one side which is the front driver's side.
When I compressed the pistions, I did not open the bleed screw but I did bleed the brakes afterwards. Btw, I don't have ABS. Even with the bleeder screw not open, it did not take too much effort with to push back the pistons, atleast not much more than the front passenger side which seems to be fine.
I don't mind replacing calipers, I just want to be sure that that's where the problem lies.
Question? Is the problem on one side or both sides?
If there is a problem with the master cylinder, both the right and left sides would be affected.
If only one side is affected, it has to be something on that side.
The evidence is over whelming that the brakes are dragging IMO.
When you compressed the pistons did you OPEN the bleed screw to let the excess fluid out? Old brake fluid should never be forced backwards through the system (esp for ABS). Always open the bleed screw to allow the excess fluid out.
FWIIW, the pistons should almost be easy to compress once the bleed screw is open.
Did you bleed all 4 wheels until clear fluid came out? Suggest re-bleeding all 4 wheels.