My latest SDL had one stuck rear caliper and the other rear would drag. I replaced both calipers with rebuilt units and also replaced the lines. The lines were 85% of the problem. They had collapsed internally and wouldn’t allow enough fluid to pass through. I installed the rebuilt calipers and while I waited on the brake lines to arrive I built myself a pressure brake bleeder. That was some of the best money I’ve spent on homemade equipment. It took less than 30 minutes to bleed the rears and change out all the fluid in the system with the pressure bleeder.