I have a 1987 GL1200 Standard. My rear brake has been dragging. I have taken the master cylinder apart and checked the small port and put a small piece of wire through it. It is clear. I have cleaned the pistons in the caliper and replaced the rear brake line rubber hose with new, flushed with new brake fluid, cleaned the slider bolt in the caliper which is free, and the brake is still dragging! Ughh! Any suggestions? Maybe time for new master cylinder or new caliper?