there is a thread on here that shows a cut away of a caliper cylinder and the rings. There is a good explaination of what happens when those rings wear to the limit and how the fluid dynamics are changed to cause a dragging caliper. I think from age and use, those cylinders can get glazed too not allowing complete piston retraction. My plan if the problem reoccurs is to get the kits and rebuild the whole calipers. I am out of ideas and thats all I can think of. New calipers are big $$$$.

I put new hoses on and that did seem to help....for now after getting that pebble out. They can act like one way valves when they are weakened and collapsing.