Did you replace the flexi brake hose on both rear wheels? The problem is that the rubber inside the hose perish over time and as fluid travells down to the flexi to the caliper, the hose opening inside is restricting the hole in the hose , and the fluid is unable to return ,so a little pressure is on all the time .So the pads never clear the disc. This is also caused by the garage monkey useing hose clamps to cut of the fluid supply, to make caliper work easy , and to stop the fluid escape ..