BDeB wrote:
There is no seal for the rod where it goes thru the floorboard and into the vacuum section of the M/C assembly, just a large felt washer.
There is a heavy rubber hose inside the vacuum booster that supplies manifold vacuum from the connection on the outside to the vacuum piston inside. If that hose is disconnected or damaged there will be a massive vacuum leak and loss of pedal boost.
Unfortunately the whole booster and master cylinder assembly would have to be removed to check this.

See Plate No.43 in the 1948-54 parts book for a cross-section view and Plate No. 13A in the 1955-56 parts book for an exploded view.
The Easamatic Power Brake section of the 1951-54 service manual has step by step instructions and photos as well. All available on this site.