You may need check the master cylinder also. Drum brake systems as on the Traction Avant have a residual pressure valve (RPV) in the master cylinder. The idea is that the brake lines are always under a little pressure, but not enough to overcome the brake return springs. The purpose of the RPV is if you have a leak it will force fluid out of the leak rather than allow air in. I recently helped someone else with an 11BL who had sourced a generic master cylinder rebuild kit and was having trouble with one of the front brakes not releasing, unless the pressure was bled from the wheel cylinder. It turned out the RPV in the kit he sourced was incorrect so it was holding too much pressure. Installing the correct RPV cured the problem.