In the interest of clarification, I have added some information to the schematic of the tape deck headphone amp that I'm having problems with.
Some circuit paths are now labeled:
As always, the points at which voltage readings are marked with a star are NOT producing the voltage indicated. The +7V location is measuring 131mV instead. The other two points where a star is indicated are measuring between 20mV and 30mV (fluctuating slightly).
I am starting to think that a circuit OUTSIDE of this circuit might be at fault, because NOTHING inside of this circuit seems to be faulty...but the darn thing still WILL NOT work.