If the Caliper Pistons are stuck all on their own when you Jack the Car up and open the Bleed Screw they are still going to drag more than they should.

I have never had any Problems with any Brake Booster on any of the Cars I have owned so I cannot tell you if the Rebuilt Power Brake Booster itself could be the cause.

On mine the Master Cylinder Push Rod is part of the Master Cylinder and is not adjustable.
If you loosen one of the Master Cylinder Lines at the Master Cylinder and fluid spurts out there it possible there is some issue in the Master Cylinder that is not allowing the Pressure to bleed out. There is passages for that inside the Master Cylinder.

__________________
84 300D, 82 Volvo 244Gl Diesel