Make sure no caps are leaking. Pay particular attention to C2, C3 and C7.
Small caps C2 and C3 - when they get old, they can disable power to the 723 regulator. What voltage do you have at pins 11 or 12 on the 723?
To see if your regulator is being loaded down by an excessive load -- measure the voltage directly across R6 -- the 0.12 ohm, 5W resistor.

Current made part number for the MC1723CP are LM723CN or UA723CN.
LM723CN was recently discontinued by Texas Instruments leaving only the UA723CN (also made by Texas Instruments).
Current made part number for the 2N6057 is 2N6284.
But these two don't just go bad by sitting idle in storage.

Pins 11 and 12 are your problem. This should not change with or without load.
Suspect caps C2 and C3 or the voltage coming from the bridge rectifier. If C2 and C3 are original - replace them.
BUT if fuse F1 or his connection is bad - this will also cause pins 11 and 12 to be low. Bad connection somewhere? Those "wonderful" Data East fuse holders?

Changing the current sense resistor from 0.12 to 0.1 ohms will increase the short circuit detection circuit & shutdown by a bit ... not enough to worry about, though.