I have an 83 Venture Royale and can't get my rear caliper to stop sticking.  I lately bled the lines using a compressed-air powered vacuum bleeder.  The brakes are more solid than they've ever been but the caliper won't stop sticking.  I've tried 2 different calipers and rebuilt one of them, polished the pins, greased everything that could need it, everything is like new on the caliper -- or as "like new" as a 33 year old caliper can be.  I also just rebuilt the rear master cylinder a few months back, took that back apart and put back together when I did the caliper just to make sure mc wasn't the issue.  I took the slave apart too, saw no issues, cleaned it, put it back together.  Everything is now cleaned and rebuilt but the problem persists.  I haven't changed the brake line but it's a stainless line, at least 3 or 4 years old, maybe older (it was on the bike when I got it).  One last thing, the caliper does release some and did before the rebuild too. When the brakes are applied the tire stops and can't be moved but when I take pressure off, the pistons don't retract far enough to keep the pads from rubbing. Although with the brake released I can spin the tire again.  Has anyone seen this before or have any suggestions?