Brake Problem 85 300D

[rmmagow]

My car has been sitting for a couple of months. I took it out today for a shake-down before putting it back into semi-daily service. The passenger side rear brake is dragging pretty badly. Pulled into the driveway and a temp check shows three wheels at around 100 degrees, the rear passenger side was smoking a little and read around 190 to 200 degrees. I had previously taken the caliper off, cleaned up the brake pins, pushed the pistons back in etc. After that the brake seemed ok. I did that about 2 weeks ago. Question, are the calipers known to rust up inside and need a good cleaning and new seals or is a collapsing flex hose the more likely issue. Pads look OK, rotor is OK and prior to putting it up this summer, all was working fine.
Thanks for any and all advice.