I replaced the rear calipers a little over a year ago. My rear drivers side seems to be dragging. I dont think it the caliper, since if I open the bleeder valve, the caliper piston pushes in. If I dont, the piston goes no where when trying to compress it. I've read about the inside of the hoses collapsing and acting like a check valve, not letting the fluid go back up toward the reservoir. Thoughts?