Brake help? BMW 78 R100S

My front brake was locked up after adding fluid and pumping them. No play in the lever. Bled them and took apart the master cylinder and cleaned it. Rode for about 10 miles and they froze up again. Was able to open the bleeder to relieve the pressure and rode home. Pumped them a few times after I got home and now they are locked up again. The master cylinder has a good sized hole (not a tiny hole in the piston) for letting the fluid back into the master cylinder so I don't think it could be blocked. Air in the lines would make the lever squishy not hard, right? Didn't think it could be the calipers because opening the bleeder valve released the pressure (temporarily) Any thoughts?

There is something blocking the fluid return. Either the MC piston is incorrectly assembled or there is crap in the lines blocking the flow.

How old are the brake lines? They can deteriorate and send crap back up to the MC port.

There are usually 2 holes in the bottom of MC's....One is to let fluid into the piston area, the other is the equalizer hole, usually close to the outlet of the MC. The equalizer hole is usually tiny, and hard to see, especially id there is any debris.