Early A Disc Brake Help Needed!!

The answer to the question was in your post. Your master cylinder is probably junk. The system is not holding pressure. So you either have a leak to the outside (which you should be able to find) or the master doesn't hold. Is the fluid level going down?

If you had air in the system you would have a soft pedal which would pump up, but then it would hold (although it might not be very hard). Also if you continue to bleed and you aren't getting air, it is a reasonable bet that air isn't the problem.

As far as bench bleeding goes, it saves some time, especially if you are filling an empty system, but once you have bled all the air out, it would seem silly to open a line. Also modern master cylinders will "gravity bleed" in time (as opposed to older cars where the master was under the floor and not the highest point in the system.) Over night should have been long enough.